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Tear Jerker: Kyousogiga
The three siblings are abandoned by their parents with no explanation given to them and each of them have their own reasons for wanting them to return:
Kurama wants to see the real world, but his dad forbids him due to not being human. Though he did enjoy Mirror Kyoto, Kurama still wants to explore the outside and told his dad that he wants to be recognized for his achievements. Sadly, when the parents left, Kurama appoints himself as the leader of the Council of Three so that he will find a way to get out of Mirror Kyoto.
Yase is the most effected with regards to her abandonment. She was very close to her mom and hoards childhood mementos that remind her of Koto. When Kurama tosses away her favorite doll to test if it could reach their parents, Yase was devastated. Every time the station opens, Yase hates the event. Though, thanks to Koto, she realized that there's still hope.
Yakushimaru/Myoe lost his family and commits suicide. However, the original Myoe resurrected him against his will and made him immortal. Though he seemed to get over it later on, his parents' departure made him bitter and eager to die once they return.