Johnny is one of the seemingly younger members of the Science Department. He is often identified by the black skull on his shirt and his big opaque glasses which completely hide his eyes. At first completely circular he has changed for more ovale ones. Recently he has started to tie his hair in a ponytail. He is a short individual with curly brown hair combed backwards. Aside from that he used to wear the typical science section uniform and a tie. He often wears headphones.
Johnny has a a rather small brown golem. It has simple ovale wings with only one section. These don't seem to be completely connected to the main body which may be the result of advanced technology. The main body is round and fluffy with the usual eye in the middle.
Johnny is friendly and amiable, but one of the weakest members of the Science Division. Prone to passing out from low blood pressure, he is taken to the Medical Division on a regular basis, initially by Tup Dop and, after Tup's death, by Tup's sister, Cash Dop. Despite all of the hatred harbored within the Order towards Allen, Johnny has remained steadfast on Allen's support side, defending him constantly when he hears rumors going around in Allen's disfavor. Because of Allen getting hurt badly while defending Johnny during the attack on the European Branch Headquarters, Johnny has dedicated himself to getting stronger so that, when Allen needs it, he can support him in return.
Johnny comes from a family of tailors. His family was apparentely not very rich. This is where his sewing skills come from. Depending to the reliability of what he says to Reever, his grandmother is currently in charge of the family buisness. 
Formerly a member of the North American Branch Science Division, along with his best friend Tup Dop, Johnny has presumably served the order for a while to have been able to secure a promotion to the European Branch, despite his age.
He was one of Suman's friends; he was the only one who knew that Suman was lonely. Because their rooms were so close together, they would often play chess together, in which Johnny would win most of the time. Whenever Suman would lose, he would ignore Johnny the next time they met in the cafeteria but always asked Johnny to a game whenever he returned from missions.
Introduction Arc Edit
Johnny observes the intruder with the other members of the science section.
Destruction of the Black Order Attempt Arc Edit
He undergoes the failed experiment of Komui: Komulin. Johnny ties to destroy the invention with a huge cannon but Komui hides his eyes and keep him from aiming correctly. When the robot is finally destroyed by Lenalee he greets Allen with everyone.
The Vampire of the Old Castle Arc Edit
Johnny discovers an investigation document about a vampire legend. He asks Reever about this who himself asks Komui. Komui tells that this had nothing to do with innocence. Johnny wonders what is the link with the book linked to the document, a book about ancient plants...
Suman Dark's Fallen ArcEdit
When he found out that Suman was dying, his face became dominated by tears and heartbroken sorrow. The manga also highlighted his presence in panels, making this particular scene one of the more emotional scenes of the series.
Invasion Of Headquarters arc
After Allen returns with the Ark, Johnny defends him against the accusations that he is a traitor working for the Noah. A short time later, Johnny is impaled through the chest by the Noah Lulu Bell, disguised as Andrew Nansen, as her Akuma forces invade the Black Order HQ. He is later thrown by the Skull Tapp Dopp and is finally attacked by an Akuma. However, Johnny is saved before the Akuma could eat him, and he begs Allen to save everyone. Johnny disappears, along with Bak Chang, Reever, the Generals, the scientists, Miranda, and Noise Marie, when the level 4 Akuma destroys the fifth laboratory. He is later shown to be alive and in stable condition. He pleads and weeps over the Skull Tapp. When Tapp dies, Johnny is in tears.
Johnny soon meets Tapp's sister Cash and seems to be overjoyed, even hugging her and screaming that she has her brother's belly, which Cash is incredibly annoyed by. Besides Bak, Reever and Komui, he is the most prominent member of the Science Department.
Seed of Destruction arcEdit
When Reever and the other Science Section heads, Regory Peck and Mark Barrows, travel to North American Branch to study the newly revealed Alma Karma, Johnny accompanies Reever as his assistant. There, Johnny becomes sickened by the revelation of what Yu Kanda and Alma had been forced to do to one another and throws up on Regory, ending in them getting dismissed from the meeting.
Almost immediately after, North American Branch is invaded by the Earl, who lets in several member of the Noah Family. The Noah take Johnny and the others hostage to lure Allen in for Alma Karma's awakening. Johnny and the others bear witness to Alma's awakening and consequential assault on the North American Branch.
After the attack, when Allen is detained, Johnny and the other members of the Science Division work on keeping up their strength so they can find a way to help Allen. When Allen escapes and Johnny hears the news that Allen has been branded a traitor and target for capture, he can only ask why it all had to happen.
Search for A.W. arcEdit
Three months after Allen's escape, Johnny has taken to working out daily and has not needed to take as many trips to the hospital as he once did. Jiji Lujun, finding this odd, drags Reever and Cash along with him to invesitgate when Johnny dismisses himself. When he is found in the off-limits records section, trying to taken Allen's case information, and he is confronted by Reever, who asks if he plans on going to Allen, Johnny announces he would like to resign from the Science Division, with his reason being that his grandmother is in ill-health due to her age and that he is the only member of his family left to carry on the family name. To keep Johnny from being punished for not taking the proper steps to resigning, though, Reever refuses to listen to Johnny's request.
Eventually, though, Reever gives in, admitting that he understands why Johnny wants to leave. After Reever and the other members of the Science Division give Johnny what well-wishes and advice they can, Johnny leaves for the train station, where he is met by two Central agents who want him to drink a serum that will cause him to forget his time in the Order. Realizing right off that drinking the serum will make him forget that he is, indeed, going to look for and help Allen, Johnny attempts to escape with the help of a few smoke bombs, but the Central agents, who turn out to be CROW, capture him quickly. Just then, though, Kanda arrives and saves Johnny, announcing that he wants to help Johnny find Allen.
After they arrive in a new town, Johnny and Kanda, using a list of people Allen/Cross owe money to, begin to go to debt collectors and building/bar managers in a nearby red-light district to look for anyone who might have seen Allen, Johnny figuring that Allen would want to find out more about Cross' connections though the places the General frequented the most. When Kanda asks Johnny why he's looking for Allen, Johnny answers that it is because he and Allen are friends, and just as Johnny asks Kanda for his reasons Johnny is attacked by an Akuma.
After being saved by Kanda, Johnny listens in shock when Kanda explains that he feels guilty for his part in Allen's transformation into Nea Walker, and Johnny, realizing that Kanda came back to the Order for Allen's sake, tears up and thanks him.
The next morning, when they are both hung over from drinking so much the previous night, Johnny tries to get Kanda to drink a newly revamped Komuvitan D, which Kanda knocks out of his hands. Johnny chases the bottle and ends up on the ground in front of a performing clown, watching the clown in wonder. When the clown holds out his hat to collect money from the onlookers, Johnny realizes that his purse was stolen and runs off, crying out frantically, to Kanda's confusion, about needing to get a job. When Johnny tries to pull Kanda along with him, the clown is attacked by an Akuma, and when the Akuma explodes before Kanda can intervene, Johnny and Kanda are shocked to see that the clown is Allen.
Johnny, happy to see Allen again, tearfully hugs him stating he's glad to have found him. Allen tries to run away only for Kanda to pin him down and rub his face with a cloth to get the make-up off. As an Akuma arrives and Allen asks how Link died, Johnny shows his relief of finally knowing that Allen really didn't kill Link. He informs Allen that Link died after Allen left prompting Allen to realize it was Apocryphos who killed the inspector. As more Akuma arrive and Allen flees to keep the people safe, Kanda and Johnny follow in pursuit. Johnny calls out for his golem and reveals it's one he made so the Order won't be able to track it and placed a receiver on Allen's head when he hugged him. When they arrive to Allen's location, Allen passes out, Kanda realizes that the wound that is bothering Allen is the one he had caused with Mugen at the North American Branch, and Johnny sees that his Innocence is trying to heal it, as it had when Tyki had punctured his heart. When Allen falls unconscious, Johnny and Kanda take him to a hotel to rest, Johnny staying by his side and urging him to fight.
After Allen awakens, Johnny is happy and gets him some water to help him. However Johnny has no drinks and Johnny tries to get some painkillers, Allen grabs Johnny's head from behind and slams it to the wall knocking him out. After Kanda rushes in the room and giving Johnny his own blood to help him, Johnny soon awakes and starts to realize what happened between him and Allen. Allen, freaking out over the thought of hurting Johnny, backs away and orders Johnny not to come any closer to him. Johnny refuses because, as he states, "Because I, Johnny Gill, as your friend..I want to help you.", which catches Allen off guard from laughing and makes Kanda smirk (and then annoyed) at the flustered Allen. They then open "Johnnys' Speedy Repair Service" to make some money and has special handcuffs on him and Allen to keep him from running away again. He tells Allen that it would be too dangerous to stay at the inn and need to make some money for their shelter and food and becomes shocked from Allen's Innocence reacting suddenly.
Having followed Allen, he sends his bat to find Kanda and let them know were they are and then he arives and is shocked to see the Earl there and saves Allen from getting crushed by the Earl. Terrified by the pressence of the Earl, Johnny attempts to get Allen away from him despite Allen's plea for Johnny to leave. Johnny refuses, stating they'll leave together. As the Earl sees similarities with Johnny carrying Allen as Mana did in the past, the Earl, angrily asking who he is blows Johnny away sending him backwards to a wall.
Johnny is knocked out by this blow and is left uncounscious for the rest of the meeting between Allen (or rather, Nea, who has taken over his body again) and the Earl. When Howard Link arrives just in time to save Allen (Nea) from the attacks of the maddened Earl, he brings both him and Johnny onto the roof of the nearby building, stating that they should hurry up and get away from the Earl while the latter restrained with the spells.
Apart from this, Johnny's image appears before Allen in Nea's subconsciousness he's currently trapped into, repeating the same words of encouragement he said to Allen in the hotel when the latter was unconscious. Also, he assures him that the bonds between people are strong and that t doesn't matter where are they and how far apart - they still remain connected. These words prompt Allen to scream out for Nea to give his body back.
In the real world, Johnny wakes up and he is released from Howard Link's spell and calls Allen's name. Nea who is controling Allen's body turns and glares at Johnny. Johnny notices Nea's golden eyes and realizes that this is not Allen. However the real Allen hears Johnny's call and stretches his hand. In Nea's inner world, he figuratively catches Johnny's hand and Nea looses control of the body. The body falls from the roof everyone watches in shock. Johnny jumps into the void to catch up Allen. Before they crash, Crown Clown is activated and hang on the calls to stop their fall. Allen Walker lands safely with Johnny and the latter joyfully realizes that Allen has regained control of his body. Allen comments that the science division always overdose even though he told him to stay away 
Allen and Johnny hug each other and cry out of relief but they are interrupted by Tyki Mikk. Johnny and Allen quickly chat about what happened. Johnny learns that Allen had no clue what happened while Nea was in control and Allen learn that Johnny was unconcious. Johnny notices that Howard Link has vanished. Tyki Mikk turns less friendly but he is fortunately stopped by a creation of Froi Tiedoll which creates a huge explosion. Allen and Johnny are blown away and before they can properly get up, Johnny realizes that something is forming around them. He tries to warn Allen but too late, in a few seconds they find themselves trapped in a coach which drives them far from the area. Johnny understands that this is General Froi Tiedoll's work and that the Black Order found them. Johnny panicks as he notes "this is bad". Allen tries to open the curtains but to no avail and Johnny explains that the carriage is made from Innocence and thus way more solid than a regular jail. Johnny them returns to panicking uttering "what do we do?" The vehicule stops and the curtains open to show Yu Kanda and Tiedoll. 
Johnny and Allen are stunned to find that they have been rescued by Yu Kanda and Froi Tiedoll in a carriage made using the senior General's innocence . Johnny is seen shocked when Allen believes for a brief moment he has been betrayed, and desperately tries to keep him and Kanda from fighting within the carriage, reminding them of their situation and if they are caught because of the two's argument, then it would be all over. Johnny is next seen surprised at the reason Allen wishes Kanda to release him, as Allen firmly believes from his ordeals that with the Order and Apocryphos chasing him, anyone near him could become a target, and does not believe he is strong enough to protect anyone. Especially a human like Johnny without innocence or abilities. Johnny is left speechless, clearly surprised at how much stress Allen had been keeping inside because of this.
When Kanda again attempts violence, believing knocking Allen out is the only way to keep him silent or from trying to run, Johnny shouts out and explains how close Allen was to giving into the Fourteenth's memory, and begs Kanda and Allen to resolve their issues another way without violence as Allen had just returned and was exhausted, alarming Kanda in doing so as Johnny grabs onto his arm. Johnny is next seen to the side as Kanda reprimands Allen's concerns and tells Johnny he has no intention of socking Allen, and lets the former scientist know he can let go of his arm. He then alongside Allen mistakes the jar Kanda shows them which is holding Timcampy's ashes as salt. When Kanda demands to know of the creature tailing them (Apocryphos ), Johnny is stunned silent at the fact Kanda has had a run-in with the humanoid innocence, and listens in silence as Kanda asks (demands) what the creature was and why it is after him.
Abilities and Skill Edit
Scientific knowledge : As the assistant of the division chief, Johnny has a vast scientific knowledge and skill. He has shown to very quickly understand mysterious phenomenons linked to dark matter or innocence that are the primary knowledge field of the Black Order.
Dressmaking Skills :Growing up in a family of tailors, Johnny has developped an ability to make clothes. He is now even in charge of the design and sewing of exorcists uniforms.
Tup Dop: Tup was Johnny's best friend. They were very often seen together in the science section,having fun and overworking. When Tap was turned into a skull, Johnny carelessly tried to save him in deny that this was too late. When he finally realized his friend's demise, Johnny was devastated. Tap spent his lasts seconds hugged by Johnny in tears. Despite him being no longer human, Tap felt Johnny's feeling and cried as well, adressing his last words to his friend: "If I could continue to live, I wouldn't care doing extra hours at all..."
Reever Wenhamm: Johnny is a close subordinate of Reever. He heavily trusts him and even made him his personal assistant. He allowed him to go with him at the Alma Karma meeting and seems to hold high hopes for Johnny. He reveals that the took him because he always had esteem for him, not only for his scientific skills but for his ability to understand exorcists and wanting to protect them. To some extent Johnny reminds him of himself. More precisely his relation with Johnny reminds him of his own relation with Komui.  In return, Johnny highly respects and likes his superior. Reever is a rather cool superior even if he can be firm sometimes. During the Searching for A.W. arc, after refusing a thousand times Reever understood Johnny 's feelings and finally let him go. Johnny was very touched.
Suman Dark: Johnny is a good friend of Suman. He regularly played chess with him after his mission and won most of the time. Though Suman did not admitted to it and was not pleased by his defeats he returned every time for a requite. When Suman died, Johnny was the only one to express his feelings at out and was deeply affected by his death.
Allen Walker: Johnny and Allen are often seen hanging together with the group when Allen is not in mission. Allen is a very precious friend of Johnny. Johnny is infinitely grateful to Allen for saving Suman and his friends later at the Order. He trusts him to the point of immediately thinking of Allen when the North American Branch was attacked by the Noah. Johnny was so saddened when Allen escaped alone from prison and he was so much worried for him that he decided to leave the Order on his own and go after Allen. Allen's bond with Johnny (and the science section) was powerful enough to at least momentarily break Nea's control of Allen's body and allow the boy to get back to the real world.
- Johnny's hobbies are repairing broken machines, chess, collecting T-shirts, sewing, and making Western-style clothes.
- He likes hamburgers, chatting, helping others, the science section, and Section Leader Reever.
- He dislikes garlic injections, power, violence, and the infirmary.
- Johnny's necessities are the tie he got from Reever, matching scrunchies with Cash, a heart that believes in Allen, and unbreakable glasses.
- Johnny is responsible for the design and sewing of the Exorcists' uniforms.