jk iinazuke to sakidori shinkon seikatsu!?

Doujin by Amairo Ayame, also knowed as High School Girl Fiancée a Head Start on Married Life.

Years ago, our protagonist saved a school student from some bullies (not without getting beaten up in the process), but as the years passed, he began to feel his life was monotonous to the point that video games couldn't fill the void. Then, a sudden call from his grandfather -who spends his time in host clubs- informs him that, having had no luck with women, he's found him a fiancée, who happens to be knocking at the door at that very moment.

The unexpected visit turns out to be the author's original character, simply called Fiancée-chan, a voluptuous, fashionable, gyaru high school girl: huge breasts, thick thighs, thick lips; fair-skinned, with long hair and the characteristic makeup of normal gyarus. She immediately proposes to the protagonist that they start having babies right away, even though they can't get married until she graduates.

Not long after, she reveals that she's the girl he saved some time ago and that she's been in love with him ever since -since she dressed very simply back then, she believes didn't call the protagonist attention, hence her change in appearance-.

Volume 1 of the story introduces our protagonists and their wild encounters.

Volume 2, subtitled "Cosplay Sex Room," introduces new characters, provides more information about the protagonists, and, as the subtitle indicates, the plot revolves around cosplay. The volume ends with the protagonist's official marriage proposal to Fianceé-chan, but not before another round of wild encounters.