Mahou - Sensou Episode 12

Takeshi and Gekkou engage in a final showdown. During the fight, it is revealed that their mother actually asked Bishop to kill Gekkou years ago—a revelation that shatters both brothers' previous understanding of the accident.

The anime ends without explaining several key mysteries, which are later clarified in the Light Novels: Mahou Sensou Episode 12

After a massive magical explosion, Takeshi wakes up back at Subaru Academy, but he realizes he has been sent back in time to the First Great Magic War. The Ending Explained (Spoilers) Takeshi and Gekkou engage in a final showdown