Tegami Bachi 2x14

Aria and Niche head to Houdai Franklin's house. Franklin attacks them upon meeting but Aria manages to convince him that she just wants to know the truth about the Day of Flicker. In flashback, Franklin was an engineer working on the airship with his friend Negich. The purpose of using the airship to travel to the artificial sun wasn't explained to the construction crew. A number of characters such as Dr. Thunderland Jr., a group of Bee triplets (with two of them serving as the gatekeeper between Bifrost and Yuusari in the present) were present aboard the ship. When Franklin wanted to steer the ship in order to get a clearer look at Akatsuki, the artificial sun gave out and flickered a few times. This momentary lapse in the sun's rays caused a huge disturbance among the crew, Franklin included, who claimed to see a monster in the sun calling for its "mother". Soon after, the airship crashed and most of them died except for Franklin, Thunderland Jr., the triplets and Balor, the general commander sent to oversee the operation. Each of them are left either partially or completely blinded. Meanwhile, Lag takes a turn for the worse and his heart energies are in danger of overflowing. When Thunderland Jr. and his staff try to stop the flow, they witness Lag involuntarily summoning visual flashbacks of his life with some imagery appearing not to be seen elsewhere before. After Lag recovers, Gauche wakes up with his memories returned, much to the delight of everyone, especially Sylvette. While Lag reunites with Gauche, Franklin tells Aria that he believes that the artificial sun is an abomination that will eventually consume all the hearts of the inhabitants and it is too late for Gauche to ever recover his lost memories.