JKとエロ議員センセイ～旧家のお嬢様JKを愛人にしてヤリたい放題～（JK to Ero Giin Sensei ~Kyuuka no Ojou-sama JK o Koibito ni Shite Yaritai Houdai~）

The protagonist is a mediocre second-rate politician from a certain ruling party.
His faction is far from the mainstream, his political base is weak, and he spends his days secretly frustrated while going through the motions of his duties. He managed to win this election, but rumors are already swirling that he might not make it next time.
He’d love to have a mistress, but he doesn’t have the means…

One day, he’s invited to a quaint inn by a local influential family to hear their request. The family head asks him to secure government funding for the region. Normally, he’d brush off such a request, but he’d heard rumors that the family had a beautiful daughter. Out of sheer curiosity, he decides to check it out. He proposes a deal: if the family offers their daughter as his companion for the night, he’ll consider securing the funding. To his surprise, they agree.

That night, he’s introduced to Hatsune, the family’s high school-aged daughter. What was supposed to be a one-night affair turns into an unexpectedly intense experience. Afterward, the protagonist decides to take Hatsune back to Tokyo as his mistress.

But here’s the twist: Hatsune turns out to be a one-in-a-hundred-million “ultimate luck charm”!
Every time they get intimate, the protagonist’s motivation skyrockets, he wins elections, his political rivals fall from grace… Will this lead to a meteoric rise to power? Well, you’ll have to play the game to find out!

[Translated from dlsite]