Also u can use the rental skill Repair Technician with your My Fairy if you've unlocked it. Just make sure your fairy is at a decent level, like 50 or so. If not, it will only replenish a little bit of the keep gauge. The extent to which the keep heals depends on the fairy's level. The higher her level, the more the keep heals. At max level (99) the whole keep heals. Hope this helps!