Mangetsu No Ou
Part of a series: 1) Mangetsu no Ou (2012) http://www.mangago.me/read-manga/mangetsu_no_ou/ 2) Zhen (2016) http://www.mangago.me/read-manga/zhen/ 3) Polar Night (2016) https://www.mangaupdates.com/series.html?id=136252
The Trigger
You'll hate Mitsui until you see his backstory with the sensei and then everything suddenly makes sense.
Koyoi Omae to
Not a fan. There is a lot of issues. Yasu was selfish, inconsiderate, and refusing to acknowledge the truth of Rikuou's feelings let alone his own. Katou...at times I think he's playing dirty. Others, he was strung along too. Yasu needed to suffer to understand Rikuou's despair and the final breaking point he reached. The way they made up didn't make any sense. Mangaka probably ran out of ideas and it shows.
KiraKira