Moe Chronicle

Upgrading a monster girl's room will allow her to earn XP from battle even when she's not in your party, and also fills the intimacy gauge a little. To do this, you will need the "Strawberry Pattern Pantie" item (can be found in dungeons, earned from battles, or purchased for 7200G in the store once you've cleared the main story), an H monster that joins your party after a battle, and some gold. First visit the girl's room in the inn and create a room upgrade item using the pantie and the H monster, which will consume both. Then back out and choose the "Rebuild" option. Each room remodeling requires one upgrade item for that specific monster girl, and an increasing amount of gold for each upgrade. The upgrade sequence for rooms is: Single - Double - Triple - Suite - Royal. This will require some grinding and will probably be one of the last trophies you unlock.