This might be kinda late reply, but the younger twin (seme) beats up the mother, and he goes to prison or something, saying that he did it because the mother would hit them (a lie). That's him talking to the guy at the end. the older twin (uke) sends him that letter, after he confesses everything, saying that it was actually sexual abuse.
No no, the older twin/uke did not go to prison. The younger twin lied and said that he beat the mother up because she was being abusive (he didn't want to embarrass his brother by saying he was raped by how own mother I guess). The guy you see being interrogated at the end was the younger twin/seme, the one who is refusing to talk
Later, the interrogator says that the older twin tried to confess everything so that the younger twin can get out of prison or something, and the older twin also writes that letter at the end.
Uke wrote that around the time he confessed so we don't know if seme was released or not (and they couldn't know it either), but uke said he would wait (in case they don't release seme). I would also like a sequel with a happy ending, but if you think logically seme can't be too long in jail because they are minors and if they believed uke's confession the reasons that lead seme to beat his mother would shorter his sentence.
I read the ending twice but can not understand what happened with the mother , the drawing doesn't make sense to me much. Was he sexually abused or brutally abused by the mother? How the hell the mother went into coma ? ><,