Warui Koto, Zenbu 

Hinako, the student council president, secretly pines for the council's advisor Yano-san. When Chibana, an underclassman on the council, finds out about Hinako's secret, he forces her into a "mutual agreement." The straight-laced council president and the scheming kouhai, all alone in the student council office after school with their shared secrets. Adapted from the winning story of the 2018 Everystar Novel Prize Betsufure Creative Award.