Mysterious girlfriend X. Volume 5

Akira Tsubaki happens to fall hard for Mikoto Urabe, who just transferred into his class. This obsession eventually leads to Akira building up an extremely high fever. Urabe claims the cause is lovesickness which only she can cure! As Akira frantically tries to work out the antidote, he begins to suspect that Urabe may not be entirely who she seems. This series is currently outperforming Vertical's other sleeper hit Ajin on Crunchyroll, and looks set to be the next hit manga series.