Thread:SageM/@comment-46530157-20201002183704/@comment-24053170-20201002184745

If you watch the episode carefully, you will see that Ashi had no idea she was able to use the same powers as Aku until Jack pointed it out.

Which means that she was using his powers unconsciously, rather than consciously.

Aku didn't forget that fact, rather he didn't realize anything was wrong until after the truth of Jack telling Ashi about her new abilities.

In fact the entire point and purpose of Battle Through Time game is Aku realizing that he could still get one last laugh at Jack before he returned to the Past.

Aku didn't forget, its just that things were hectic due to being in the middle of a combat situation.