Made in Abyss Movie 1: Tabidachi no Yoake

Riko lives in the city of Orth at the edge of the Abyss and dreams of becoming a great Cave Raider like her mother Lyza, one of the legendary White Whistles. During an expedition in the upper layers, she discovers a humanoid robot boy with no memory of his origin, names him Reg, and hides him among the orphanage students.

A message later suggests Lyza may still be alive at the bottom, so Riko chooses to descend with Reg even though going deeper makes returning increasingly impossible. They reach the Second Layer and meet Ozen, an old companion of Lyza who offers no comforting answers. There Riko learns a shocking truth about her own birth and discovers that the road toward her mother will test whether she can survive long before it gives her any answers.