Wonder Beat Scramble (1986)

Original title: ワンダービートS

The 13-year-old Benny's father has mysteriously disappeared on an expedition to Sirius. Almost at the same time, attacks start from the alien intars to the Earth dwellers. They implant themselves in the bodies of the inhabitants of the earth. Due to the mysterious disappearance of Benny's father, he is accused of making common cause with the intars. Benny, who has remained behind, suffers greatly from these accusations and hopes one day to be able to unravel the mystery of his father's disappearance and that of the intars. He joins the "White Pegasus," a special unit to combat the Intars and fight together with them against the aliens in the human body. For this, they scale a spaceship down to microscopic size and infiltrate it into the infested body.