Does Not Know His Own Strength : After rewriting himself before the story begins, he began breaking stuff on accident if he doesn't watch his own strength. Gaia uses it as a storage facility for their familiars, since the other way for keeping familiars in the regular world is to keep them in fridges because familiars are made from perishables, and the magic apparently leaks there from Kazamatsuri.
Power Incontinence : When she was little, her control over her ability was not as refined and she accidentally wiped herself from the memory of her parents.
QuillBot can also function as a grammar checker and fluency enhancer.
Healing Factor : Not most of the time, but in an area filled with the poison she makes she possesses a healing factor even stronger than Shizuru's. Besides that, the small plant was the only life on the Moon.
In general and on a lighter note, the story occasionally admits that the other girls are interested in Kotarou as well, but they're always supportive of whichever girl's route it is rather than getting in the way. Sakuya might not even be truly dead, either.
Meanwhile, both Guardian and Gaia are preparing for a confrontation during the Harvest Festa. It's actually something that's sometimes criticized about Terra route, because some of Terra Kotarou's acts are 'programmed' rather than derived from his own free will.
Mundane Utility : Kotarou decides that the blades he can manifest from his wrist are not suited for cooking. Don't You Dare Pity Me!
Shortly afterwards, the same thing happens to Sakuya, which seems to be a lot more appreciated.