I would say Yashiro thinks this is his only way to save everyone. He considers himself to be the only expendable person. I believe he called his cop buddy and maybe will try to turn himself in for the murders to clear any Doushinkai involvement, asking Misumi to cut ties with him will prove Misumi's disapproval and clear his path to leadership. But ONLY Yashiro thinks Yashiro is expendable. Everyone else loves him. So the strongest person he has right now just kidnapped him. Way to go Doumeki! Missed you, you beautiful heavy tank!
you are a real fun, asking why he beats up nanahara, this wasn't the first time he hit him dude, that was kinda fatherly punishment and saving him. just read their conversation again. in yakuza world you show your care for your underling like this, of course if you are yashiro not hirata.
Not suicidal but sacrificial if that is a word? He beats up Nanahara to prevent him from following him. Nanahara knows what his boss is doing --- leaving him behind to protect him -- because he knows Yashiro by now.
Yashiro probably is resigned to the idea that he is not going to get out alive of this or the Yakuza life for that matter and he intends to go out alone and keep safe the people he likes --- from Doumeki to Misumi and his subordinates. It is of course a suicide mission because alone he would have no chance out there -- Chesnut and the other hired gun have no allegiance to him and won't put themselves as shield to save him.
But of course he underestimated Doumeki ... the 'little bird' is resolved to stay by his side and not even Yashiro can't stop him.
Why does he beat up Nanahara? He calls to cut ties with Misumi? Where is he going? Is he possibly suicidal? Chestnut might be the short man that helped out before but what is he thinking?