Kyoushi to Seito to

Kyoushi to Seito to is a 2005 Hentai Romance manga by Fuuga.

Daisuke Nishimoto is a high school student who lives alone while his parents manage an apartment complex. His homeroom teacher, Mai Morisaki, was recently evicted from her apartment and wants a place to stay. Nishimoto, however, refuses to try to convince his parents to give her a spot. Mai, however, doesn't give up on trying to get something from him. She ends up invading her house and sleeping on his bed, and he reluctantly accepts her stay. But it doesn't take too long until the sexual tension between them reaches a level inadequate for student and teacher.

Serialized on Comic Mujin.

Tropes used in Kyoushi to Seito to include:

A-Cup Angst: Saya apologizes to Nishimoto while having sex because her breasts are small, which makes him comfort her.
Amicable Exes: Fukuhara Saya, Nishimoto's ex, is in friendly terms with him.
Animal Motifs: For Morisaki, it's the cat. Not only because she infiltrates inside Nishimoto's house and do things like she wants inside him, but she also visibly hisses when annoyed.
Brother-Sister Incest: Between Aito Ichishima and his sister.
Cerebus Syndrome: Starts like a wacky comedy. By the last chapters, Nishimoto had raped Morisaki in a jealous rage, Nishimoto suffers and a murder attempt and then both him and his teacher have to sacrifice their life in the school to ever get a chance of being together.
Four Eyes, Zero Soul: The vice-principal, who wears glasses, is eventually revealed to be a violent, manipulative, would-be-rapist.
Hot Teacher: Morisaki is pretty curvy and pretty. As is Aito's sister who is also a teacher.
Interrupted Intimacy: Chapter 6. The couple gets caught, dressed but with Morisaki's on top of Nishimoto, by a group of Nishimoto's friends who had just left and wanted to return a key accidently taken.
Making Love in All the Wrong Places:
- The couple ends up having sex inside the school in chapter 2.
- In chapter 4, Aito's sister masturbates him in the school right in front of Morisaki as a twisted way of showing they do have a more caring relationship than Morisaki and Nishimoto.
Karma Houdini: The vice-principal manages to get away with pushing Nishimoto down a flight of stairs and basically forcing Morisaki to resign or having sex with him.
One of the Kids: Morisaki tends to act very childish, especially when she is envious of Nishimoto.
Rape as Drama: Nishimoto ends up raping Morisaka at the end of chapter 6, angry at the prospect of her departure. They end up reconciling as he brings her to a walk in the beach, and she gives up on leaving his apartment. And after he accepts a lot of slaps and kicks.
Shameless Fanservice Girl: Morisaki dresses skimpily inside Nishimoto's apartment like it's her own house, wearing loose shirts, no underwear, no bra, or a combination of the three.
Star-Crossed Lovers: It seems like it until at the last minute is averted. Nishimoto and Morisaki stay separated for one year, despite being able to meet, with Morisaki rationalizing they could find other people in the meantime, only for her to finally decide to come back to him.
Teacher-Student Romance: Eventually it goes from sexual attraction to romantic.
Who Wears Short Shorts: Though her wardrobe tends to change, Morisaki often wears short shorts inside Nishimoto's apartment.
Your Cheating Heart: Though his sexual drive makes him move along, Nishimoto is clearly not comfortable with having sex with Saya because of Morisaki. He consciously avoids ejaculating inside her. Morisaki however never discovers they went that far.
Zettai Ryouiki: In the cover of chapter 2, Morisaki wears a type B.