Michi no Toki

Michino Ryokō Toki ( Unknown Time Traveler 未知の時旅行 Mii-Chee-No Ry-Oko Toe-Kii ) 

In the anime, she also appears as a cameo in the episode "One With Time" where the cast meets with the Lore Masters. They all introduce themselves except Michino, which is why some think there are only 12 Stone Masters when there are in fact 13. You can see her sitting beside Kurea, master of the Stone.

Though that doesn't matter, since she is supposed to be a main character in APOCA: Origins.