Cosimov is a jealous and vicious individual. He has no qualms using others to achieve his goals. He is manipulative and violent..
Cosimov was the star performer of the circus troupe. One day (shortly before the holidays) Mana arrived and his performance with his dog allowed him to take his place as best performer. Jealous of Mana and Allen (the dog) always being famous. He told Red (Allen Walker) to feed allen (the dog) glass, when Red refused Cosimov beat him.
Later he decided to kill the dog himself by beating him to death and to charge Red for it. He acted in front of the other circus member into believing Allen was guilty of killing the dog. Red attacks him out of rage but Cosimov exaggerates his injury leading to Red being taken by the troupe members. Allen rushes back towards Cosimov but he is stopped by Mana.
Later the Earl attacks the circus with a number of Akumas. Cosimov is killed during the attack.