Kaho, Minamo Historian keeps track of the cards she exiled for as long as she remains the same object on the battlefield. Changing control does not cause her to become a new object, so she will remember the cards she exiled, and her new controller will be able to utilize said cards.
October 2, 2017 5:02 p.m.
Ok, and so... when he gains control of her, does he searches for instant cards as well?
October 2, 2017 5:13 p.m.
No, she only searches when she "enters the battlefield", which does not happen when she changes controllers, unless they were to cast something like Cloudshift on her afterwards, in which case she would become a new object, and "forget" the cards she previously exiled.