Masou Gakuen HxH: Season 1, Episode 4
A huge enemy fleet is bombarding Ataraxia, led by a battleship with a gigantic cannon. Amaterasu does their best to fight them off, but Aine's Hybrid Count is critically low. Kizuna is able to rescue her in the nick of time and take her back to Ataraxia, where he talks with her about her past. He finds out that Aine was also a test subject in Dr. Nayuta's experiments, and that she knows the key to unlocking her lost memories: a more advanced version of the Heart Hybrid called the Climax Hybrid.