Shitai o Arau

A 2002 Hentai Visual Novel by Silky, Shitai o Arau (it can be translated as Body Washing) is about a young man whose job is to wash corpses.

Our protagonist, whose name can be changed by the player in the start menu but by default has the surname Yasaka, is a high school graduate who failed to enter college the first time. He is working part-time on a university hospital under the guidance of deputy director Chigusa Tsuyuzaki until he can take exams again. The other directors, however, find about him, and do not want someone who isn't even a medical student working at the hospital. Chigusa, however, finds a loop hole and gives Yasaka a job whose requirements are minimal: washing and cleaning corpses donated for research.

Yasaka is taken aback by the morbid nature of the job, but goes along anyway, helped by the fact Chigusa is very supportive of him. Surely nothing can go wrong. They're just corpses.

Published by Silky's. It was adapted into a three-episode OVA in 2003.

Tropes used in Shitai o Arau include:

Awful Truth: Ending 20. Yasaka has killed Yuuki in his madness, something he blocked of his mind. He discovers the body on Chigusa's room in the hospital and goes ballistic, killing every co-worker with who he had close contact with.
Babies Ever After: In the good endings of Miwako and Mao, Yasaka and them have a daughter after the hospital incident is over.
Bait and Switch: The whole "corpse washing" business has little plot importance, but does make Yasaka stressful thanks to error or unusual circumstances.
Big Bad: Chigusa, who have been experimenting on Yasaka all along with a drug that enhances vitality, but also aggressivity.
But Thou Must: In the fifth day of Chigusa's route, there is no option to refuse Chigusa's blue pills.
Cain and Abel: Chigusa and Yuuki are sisters. Chigusa is a Mad Scientist who experiments on people, Mido is the nurse who tries to make Chigusa stop when the experiment with Yasaka seems to be going too far for her.
Downer Ending: Ending 20. Yasaka has killed every named character except Shizue and Miwako in the middle of his madness and, even without the drug, he has been reduced to a raving animal reduced to grunt "Kill", "Body" and "Washing" repeatedly. The only positive point is that the police discovered that a new drug was responsible for it and can stop possible new cases, but does not lesser the fact everything realistically could go wrong went wrong.
Driven to Madness: Ending 20. Yasaka took so many of Chigusa's blue pills he turned into a raving murderous animal. He is kept on a very tight cell with only small openings to the outside for food and air, with prison guards warned to keep distance from him to avoid being in attack range.
Establishing Character Moment: You find Kirita harassing Mao to go out with him when you first meet him, establishing he is a Casanova Wannabe Jerkass.
Fat Bastard: Shinjirou Kita is an annoying jerk to say the least, with a considerable gut.
Genre Shift: Until the fifth day the game is kind of a Slice of Life. A slice-of-life with corpses. Then things turn a dramatic turn to Psychological Horror.
Hello, Insert Name Here: You're asked to name yourself every time you start a new playthrough, with the surname Yasaka already there in case you don't want to.
Hoist by His Own Petard: In the path to ending 20, Chigusa keeps Yasaka working in the hospital even after he had killed Mido after taking a pill. He ends up killing her.
I Love the Dead: Invoked but averted, though Kaburagi likes to joke about the concept, calling Yasaka lucky when he have beautiful female corpses to handle.
In Love with Your Carnage: In the path to ending 20, Chigusa has sex with Yasaka while Mido's corpse is still hot on the same room, and is enamored with the fact he killed her.
Mind Screw: In-universe this is what Yasaka thinks it's happening to him in the second part of Chigusa's route. Any attentive player will notice his hallucinations only start again and again after he takes the blue pills Chigusa offers to him however, so no matter how disturbing the hallucinations are the player knows exactly what is happening and the trope is averted.
Power of Love: Possibly defied by Chigusa in the seventh day of her route, where she will mock Yasaka for thinking she knows so much about him because she loves him, if he picks that option from a list of three possible answers.
Rapunzel Hair: Mao's hair goes down her waist.
Reality Ensues: Ending 20. Yasaka turned into a crazy murderous animal but he is still just a civilian and stands no chance against well-trained police agents. The cops capture him and put him on a solitary cell with little to no openings, and the television anchor do not mention even a wounded cop, indicating that once the police came for him they apprehended him very easily.
Shoo Out the Clowns: Shizue Kamata, a domestic housewife who teases Yasaka about his romantic relationships and tries to cheer him up, disappears from the plot after the fifth day, where things get considerably more serious.
Slice of Life: Until the fifth day, the game has shades of this, as is basically Yasaka trying to costume himself to do a gruesome job without nothing particularly odd happening.
Token Loli: Mao. She looks way younger than her age indicates, has a small chest, a very acute voice, and is only one-hundred-fourth-five centimeters tall.
Unknown Rival: Yasaka seems to barely know Kirita exists most of the time through multiple routes, though he is always polite towards him.
Urban Legends: Based on one in Japan about a supposed part-time job of body washing, who also supposedly pays very well and, more importantly, does not need a degree. As you may guess, the last two characteristics result in hospitals getting a lot of annoying telephone calls asking for a job that doesn't exist. In real-life, if it is even necessary, body-washing is done by morticians or students of medicine under the supervision of a teacher.
Walking Spoiler: Much of Chigusa's characterization on her route only comes after she is clearly driving Yasaka mad with the blue pills.
Youthful Freckles: Mao looks and sounds much younger than a nurse officially employed a hospital, and has freckles on her nose.