If you doubt Reiji feelings for Chako let me tell you something interesting... The author designed a fish specifically for Each character you can see them in this manga art menu. When Reiji argued with Gen and he said he can't die yet bcause there's someone he loves, and Reiji wanted to see the girl again there appeared a drawing of fish in the panel, a symbol of character with specific Fin and tail patter . Now go see the manga Art and compare which fish with the same tail pattern ITS definitely not Nagi's because Nagi's fish has a straight pattern tail just like her aura. Also to explain why Rei wanted to burn the house, I think Its like the mouse accident, he think Its better to end Chako pain right away and do suicide together. That's why he say goodbye while looking at names who was searching for him (including Nagi i think Nagi called him ) i don't care about the angst, Reiji you do you but just please don't let Chako die like why she die what she did so wrong 😭? She don't even got the eggs yet