About the credit page:
Koito didn't "cut the rifle", the rifle was already cut last chapter, when Kiroranke used his rifle to block Koito's sword. The sword cut deep and got stuck in the rifle's stock.
Nolonar is correct. That rifle is just a random Mosin-Nagant Kiroranke took from a random prison guard, not his personal weapon. If Koito wanted to ceremoniously cut something, he'll cut Kiroranke's Makiri. He's just retrieving his Sabre.
Never have I seen a fight to the death in a manga where I so sympathize with all involved and yet they are truly opposed without "misunderstandings".
Kiro, you truly deserved your death but also my F.
Rip in piece you manliest of men.