Ayashi no Hakoniwa ni Ukabu Tsuki
Sane love, short story, teatcher+demon student
Shukuchoku Shitsu ni 2-ri Kiri ~ Moto Yan Kyoushi wa Sekkusu mo Yanchadeshita
Short story, no plot, start of relationship. Two teacher ex schoolmates, male and female. She looks too young.
A Kiss After 15 Years
No sex, only kissing between two teenagers
Nirameba Koi
Green flags, bad art. Vol 2 ch 10-11 (2 childhood friends who becames lovers) and another previous ch (student + school janitor) are other stories. The main story is between two students.
Orange (takano Ichigo)
A really warm-heart friendship story, with a group of teens trying to save their friend from suicide (they know about it from letters coming from the future). Chapter 23 and 24 are missing. You can find a link in the comments section with them.
Tiger and Tiger Gourd
No sex, green flag, sane love. Smart calm cool student who dislikes to be part of a yakuza family + ex punk messy student. The second blackmails the first to oblige him to tutor him.
Sakamoto desu ga?
Sakamoto first year at highschool. He's good at everything (sports, cooking, drawing, studies, friendships), always calm and cool. You don't know where he comes from, and there're hypothesis about his death after the end of the year.
Wagging the Tail Webtoon