The Melody of Oblivion S01 E10 Unicorn Series

Bocca meets up with his old friend Tsunagi. Tsunagi tells to Bocca about the Space Fort named Mitranome, and about 'Engine One'. The team intends to destroy Engine One, but Bocca wants to save Sayoko first. The team then splits into two. Bocca, Coco and another team mate goes to save Sayoko. The rest sets off to destroy Engine One.