First question:Actually, the two didn't have a grudge, mainly because it was Kiryu who was supposed to build the group, but because Kiryu took the blame, Papa Kazama let Kamiyama build the group in order to pave the way for Kiryu, but Kamiyama was really a man who didn't have much to build on at that time, and Papa Kazama also gave him a group of subordinates who were not easy to manage. And at that point in time, his sister became seriously ill and needed a large sum of money, causing him to do something against his morals. People around him are blaming him, and always say Kiryu is so much better, you see how you do this, Kiryu do it will not be like this balabala. and Kamiyama was told that he was arranged for Kiryu a stepping stone to the top of the mountain. He blacked out a little bit under extreme resentment. Especially since his sister ended up dying ......
2, Mashima wanted to be himself, and the girl he put his heart on led a peaceful life and regained her sight, and with someone who loved her and took care of her, Mashima had nothing else to worry about. So, love how it is how it is (⊙v⊙)
About the blackening of Kinsan, welcome to Kisaragi, which adds Kinsan's memories of the killings at the beginning of each chapter.