Hrm. Writer Sin: Flashbacks happening too soon. You need to cultivate the charactes a bit, first, before do flashbacks. This way the readers are more vested in the characters and will actually want to know more about their background.
It'd be different if they just went over what happened in the past in brief like they were at first. But we're only technically past the exposition here - where the characters have been introduced and the starting problem has been revealed. (That is, Shin getting kicked out of the party and what is he gonna do now?) A course of action on the characters' parts hasn't even been decided on yet, so this is no time to be reflecting on the past.