The Most Forbidden Love in the World

The Most Forbidden Love in the World (Sekai de Ichiban Dame na Koi) is a 2007 Visual Novel.

Osamu Yoshimura is an office worker that was fired by taking the fall for a financial fraud that would ruin his company's whole image. While wandering the streets, he is comforted by Hinoka Hinosaka, and mistakes her niceness for love. He ends up going after her, only to find she ran off with another guy and abandoned her daughter and her boarding house.

Said daughter, Mitoko, refuses Osamu's help at every step, despite the fact she is having problems paying property tax and the fact she is a middle school student means she wouldn't even be alone like that. Osamu does end up getting a job, but suspiciously nobody else but him and a pretty office lady called Kaya Amagi show up to work, and they receive constant phone calls of unsatisfied clients. To top the cake, Osamu gets a proposal from wealthy heiress Himeo Sawashima while going to work to leave the boarding house.

Developed by HERMIT and Regista. Initially an H Game for PC, it was ported for PSP with obviously all erotic scenes cut. Published by HERMIT and BOOST ON in Japanese, and by MangaGamer on English.

Tropes used in The Most Forbidden Love in the World include:

Bare Your Midriff: Himeo wears a crop top which exposes her belly.
Blatant Lies: In a scene on Episode 3, Yoshinori says no one on the room was born on the Heisei period. Except Mitoko is fourteen/fifteen at best and on the room, so she must have been born in the reign of emperor Akihiko if the game is set on his year of release of 2007.
Born Unlucky: Osamu seems to suffer from a series of misfortunes even before the proper beginning of the story. His father was absent during his early years, his absence was because he had several mistresses, resulting in bad blood between them, his first marriage ended in failure because his wife wanted to pursuit a professional career, and he took the fall for a fraud he did not commit. He is also allergic to Japanese food which, considering he is a japanese living on Japan, means he is pretty much surrounded by poison and has to pay a lot to eat food he can digest.
Casanova Wannabe: Tsuyoshi thinks he is irresistible but trying to flirt with Mitoko is like trying to hit a wall with a tennis ball, and no one else is convinced his efforts will generate any fruit.
Cool Old Guy: Kihee Uesaka. He is on retirement age and gives genuine help to Osamu and Mitoko.
Dogged Nice Guy: Mitoko basically ignores Tsuyoshi's attempts at flirting.
First-Name Basis: Mitoko forces Himeo and Osamu to go into this in episode seven to make them more friendly to each other.
Foreshadowing: Himeo gets very uncomfortable wherever other characters notice how uncommon her devotion to Mitoko is, and in episode 7 outright brings the possibility to Mitoko that her father may have a second family and that is why he isn't around, instead of dead as Mitoko believes. She is part of that second family, and she is so devoted to Mitoko because she is her sister.
Going Commando: During the sex scene at a public park in Kaya's route, Osamu discovers she isn't wearing panties under her kimono.
Hot Mom: Honoka is pretty and busty.
Hot Teacher: Asami, Mitoko's homeroom teacher, is pretty and curvy.
Lolicon: At the end of Kaya's route. She invokes the trope name when Mitoko appears on the room where she and Osamu were making out, calling her Osamu "made-for-lolicons' wife". The English translation changes to a shout-out to Fatal Attraction, despite the audio still being clearly audible.
Making Love in All the Wrong Places: In Kaya's route, she and Osamu end up having a sexual encounter on a public park.
Motor Mouth: It's not obvious at first, but Himeo often crams as much as words possible when given the turn to talk and is finished as quick as characters with half of the vocabulary.
OOC Is Serious Business: In episode 7, Osamu gets uncharacteristically annoyed because Himeo is interfering in his tutoring methods towards Mitoko.
Pair the Spares: In the endings where Osamu ends up with Mitoko, Tsuyoshi and Rinko hook up.
Rapunzel Hair: Himeo's hair is waist-length.
Running Gag: Mitoko slapping Osamu, most of the time for things he has no control over.
Self-Deprecation: In episode 5, Osamu gets a job as a hentai visual novel illustrator. The developers are portrayed as greedy bastards which don't care about art quality and work their employees to near-death.
Shameless Fanservice Girl: Kaya has no problem walking around Osamu wearing a loose shirt, bra and panties.
Spoiled Sweet: Himeo is pretty wealthy but it's a pretty nice girl and wants the tenants gone and the boarding house so she can take Mitoko under her protective wings.
Too Kinky to Torture: Kaya outright says when she and Osamu are at the love hotel that she would enjoy even if he hit or strangled her.
Wise Beyond Their Years: Zig-zagged. Mitoko is clearly being able to take care of himself, but she clearly doesn't recognize her own limits and how she can't keep being a student and a house lord at the same time.
Wrong Genre Savvy:
- Himeo thinks she is in some business/crime drama where she is the Villain Protagonist with only some Pet the Dog moments. This a light-hearted romantic comedy, and she is a Love Interest.
- Tsuyoshi thinks he is the protagonist of a sports/romance middle school story. He is not far of the romance, but misses all the other points, and misses the fact he is the Plucky Comic Relief.
Younger Than They Look: Mitoko is remarked in-universe to be younger than she already looks, in no small part thanks to being only one hundred forty-four centimetres tall.
You Have Outlived Your Usefulness: Osamu goes under one of this in his second job: Kaya's unnamed uncle employs him to give an appearance that his business is legitimately working while he puts his assets elsewhere to build a new one, in a kind of false bankruptcy scheme. He then fires Osamu when the company finally goes under.
Zettai Ryouiki: Mitoko wears a rank S on her middle school uniform.