The Quintessential Quintuplets Vol. 5 (manga)

THE REASON WHY

After an eventful school trip, Futaro has come down with a cold. But as the private tutor to five sisters in danger of flunking out, he doesn't have a moment to waste, and not even an illness can keep him from trying to get the quints to study! One day, a heated disagreement drives a wedge between the girls, and he's caught in the middle. Will Futaro be able to help solve this difficult problem, or is he just an unnecessary part of the equation? And, just when he's about to hit rock bottom, Futaro's past catches up to him...