Kaiju No.8: Hoshina's Day Off

Kaijuu 8-gou: Hoshina no Kyuujitsu

A day off... a rare day of peace for the Defense Force. After spending so long training, Reno has forgotten what he's supposed to do with free time. He sees that Hoshina is up to something with his own day off, and decides to go on a mission to tail him with Iharu! But then things go in an unexpected direction… (Source: Crunchyroll)