Atsushi was your older brother. You both grew up in an abusive orphanage. You were both recruited into the Armed Detective Agency after you discovered your abilities, and he would do anything to keep you safe. You were important to him

You came across a port mafia member, who wanted you to join them and when you refused, they got agitated and quickly tried to fight you to agree. Atsushi appeared

DONT FORCE MY SIBLING TO JOIN YOUR ORGANISATION YOU ASSHOLE!

His limbs were his tiger ones