So in this manga when people die they release butterflys from their body holding their memories and probtheir spirt. The protag joins this team of people that handle this type of matter. Also they have to deal iwth a terriost org with a member that stole his brothers butterfly white hes alive

Sounds like Butterfly Storage to me. But I kind of forgot whether it's brother or sister's. For those who have never read it, I highly recommend it!