An alien that sucks inside all things.
Sokonashi-seijin (底無し星人, Bottomless Alien) is an alien who devours everything in his path, including Kinnikuman and Natsuko. Kinnikuman eventually escapes after cutting Sokonashi-seijin's stomach open with his Kinniku Cutter. He later reappears as one of Kinkotsuman's minions.
Sokonashi-Seijin is seen first sucking in random civilians from the street, including Nakano-san, and - immediately after - Kinnikuman's hut from Beverly Park.  The act of removing the hut angers Kinnikuman, and Meat Alexandria explains that the monster has a bottomless stomach and will swallow all that it encounters. It removes Natsuko's clothes with the force of its inhalation, and takes Kinnikuman and Natsuko into its body. 
Inside its body is almost luxurious, as it has sucked inside various hotels and shops and world landmarks, but - on the downside - its gastric juices kill anyone that comes into contact with the liquid all around them. Sokonashi-Seijin falls asleep, while Kinnikuman and friends try to escape. The gastric acid gets higher and higher inside the stomach, but Kinnikuman eats some garlic and grows large, and is able to cut open the stomach from the inside. He bursts out of the dead Sokonashi-Seijin and saves everyone's lives. 
Sokonashi-Seijin is not seen again, due to death. 
- Submitted by: Katsuzo Nomoto from Kagoshima