You basically just have to keep getting "critical"s when you touch him or whatever. My strategy was basically just to cycle through all the options until I got to 100% / 5 hearts. It's so hard because it doesn't tell you what you're meant to do, so you just have to guess. :c
Have you tried...
I just finished Seiji's route, and I spotted an error (?). During his confession, he says:
When it should be:
Also, his ADV events are so sad. Especially "His Situation". I wanted to hug him so bad. :c
I made an account just to say thank you! You are an amazing team, and I wish I could hug each and every one of you.
Thank you so much for translating this so us non-Japanese can play!
(I also noticed that you translated all the katakana (?) sounds! I was hoping you would.)