I just realized that the sugar in the doughnuts and mayonnaise may help replenish mana.

No, Haruto is just simple and Mayonnaise-san is just weird.

At least give my theory a chance.

Actually, all Haruto needs is food and sleep to replenish his mana. Plain sugar donuts just happen to have been his favorite since childhood, as seen in his flashback in episode 9.

Really liked this episode. I absolutely loved the character development (gasp!) they gave Phoenix, and while I know a part of me was really hoping this was the start of a face turn for him, I am glad that it took the direction it did with him taking the advice in his own twisted way and going rogue.

Haruto definitely had a bit more personality to him the last couple episodes as well, though this was your standard mid-season powerup affair. Also really liking the dragon timer, though this isn't quite how I thought it would work, I thought the all-dragon form or whatever was basically him with the power of all 4 dragons equipped *shrug*.

Also really don't think your theory holds too much water AoBlue, sorry. There's just nothing that really supports it beyond Phoenix saying that he doesn't get the taste of donuts.