Zeru is an alien from a planet located 220 years light away from the Earth in the Sagittarius constellation.

His species is red-skinned, horned, and has centuries-long lifespans. Zeru's planet was conquered by the Efy Dolgh, and he wanted to prevent the Earth from facing the same fate. Arriving in Japan 450 years ago, he attempted to stop the Efy Dolgh force which massacred the Washiba Clan, but the humans believed he was a demon and attacked him. In the recent past, Yukina's father Takehito Shirahane met him and attempted to assist his cause. Takehito also gave him the name Zeru as a shortened form of his full name. In the present day, he has come to the aid of UN forces in order to counter Efy Dolgh's invasion.
(Source: Wikipedia)