This is the Golden Deer house from Fire Emblem Three houses in the Garreg Mach Monastery, only male students are allowed and their teacher Byleth is encouraging them to grow fat like him spending their classes training and learning ways to gain weight. This is your first day and everyone is giving you a warm welcome despite noticing how thin you are compared to them.
The characters available are Claude, Raphael, Lorenz, Ignatz, Male Byleth among other male students