1-3) Suwa is the student whose love is unrequited for his teacher- Kannagi-Sensei. Kannagi-sensei is handsome and gentle, with a voice that instantly arouses Suwa. Contrary to appearances, the teacher who looks like he has everything all together is actually an untidy person with no fashion sense, so Suwa must come to his classroom to take care of him. However, since Suwa has passed his class with flying colors, this relationship will soon be over. But on the last day of school, Kannagi-Sensei suddenly says “I thought you loved me?” and forcibly kisses Sawa!? The dual-natured sadistic college professor and the student he’s toying with- their thrilling love story<3
From Fujoshi Bitches

4-6) Shinobu's dad died and left him to grow up under the yakuza boss. He got along well with Jin, the boss'es son, till he suddenly went to study in America, saying he can't treat Shinobu like a kid brother anymore. When the boss fell ill, Shinobu took it upon himself to lead the group, against his father's and boss'es wishes, But now Jin comes back and wants him out too?