Soukyoku

The oldest of the twins, Ikurou, is at the top of his year in academics. While the younger brother, Akaya, is below average, and Ikurou holds a superiority complex with him. However, when he feels Akaya’s gaze on him, he is reminded of what happened five years ago, when Akaya asked him, “Can I touch you,” and Ikurou feels driven into a corner. When he finally snaps and scolds Akaya, he just casually changes his lifestyle and says that he will surpass his older brother in grades. And thus a bet is placed, with the promises of a reward...

(Source: Hoshikuzuu Scans & Fujoshi Bitches & Must Be Endless)