Kokoro Connect Volume 3: Kako Random

Cultural Research Club, more like Babysitter's Club! Winter break is here, and it's nearly time for New Year's festivities... but there's a new troublemaker in town, and its name is «The Second». This time, the members of the Cultural Research Club—minus Taichi—are chosen at random to physically regress into younger versions of themselves from 12 PM to 5 PM every day! Tensions build as old, painful memories come to light. Meanwhile, Taichi is forced to keep quiet about «The Second» or else it threatens to make things even worse... Can they last until the clock runs out? Find out in volume 3 of the hit ensemble dramedy light novel from award-winning author Sadanatsu Anda!

[From J-Novel Club]