The story goes (from the Pixiv dictionary article, CMIIW)...
In the Earth Defence Force's training room, suddenly an alien showed up from the locker. The alien is hungry, so Matsumoto Hitoshi offered it Baum Kuchen, which the alien rejected.
Then, Tsukitei Housei offered sweets, which the alien accepted. They touched finger and the alien's finger glows. The alien says "Housei, my friend" before leaving back into the locker.
Later, the aliens suddenly declared war and attacked Earth, but mankind managed to stop them. Chouno Masayoshi, the commander, managed to capture an alien leader intruding the base.
This is that alien from before. Through interogation, the alien told them that there's a traitor who gave out information to the alien. When touching finger with this human, the alien's finger will glow.
So all the five crews are tested. Housei is the last, and like before, the alien's finger glows, confirming that he's the traitor. Chouno slapped him in the face.
Housei tried denying that he's the alien's ally, afraid of getting slapped again. But the alien said: Housei, my friend
Admiral looks like a bad cop waiting for the criminal's confession. And screw what it's parodying, Wo locked and saying "Tenryuu my friend" breaks my heart.