Re:ZERO -Starting Life in Another World-, Vol. 29 (light novel) - Shinichirou Otsuka

THE MOST DANGEROUS GAME OF ALL: HIDE-AND-SEEK!Subaru’s party has traveled to the Demon City of Chaosflame to recruit Divine General Yoruna Mishigure, only to run into another Divine General—the venerable Orbart—as well as someone else claiming to be the emperor of Volakia. Things only get more complicated from there, as Subaru, Al, and Medium wake up transformed into younger versions of themselves. They quickly discover the only hope they have of returning to normal is winning a city-wide game of hide-and-seek against a man who loves breaking the rules!