Manten is a Thunder Demon and the younger brother of Hiten. Manten's head resembled a cross between a shark and a seal, and for some reason his lack of hair really bothered him. You'd think when you're a mutant sheal demon you'd have bigger appearance issues to deal with. Apparently the reason why Hiten looks human and Manten looks like sea life is that their parents were two different types of demon. Hiten took after their father and Manten too after their mother.
Despite his ridiculous appearance, Manten is a very powerful demon. As half of the Thunder Brothers, he and Hiten kill an entire army. With the two Shikon Jewel shards Manten possesses, he's able to fly via a cloud and also breathe lightning. He and Hiten are also responsible for killing Shippou's parents in order to get the jewel shard they possessed. In fact, Manten wore Shippou's father's pelt as an ornament and used it to taunt him.
It's right about then that Kagome saves Shippou from Manten by shooting Manten with her blessed arrows. One of her arrows cuts off two of his hairs. In order to set things right, he kidnaps her to make hair tonic out of her. Hiten decides a better use for her would be to use her to get Inuyasha to come fight them.
At that fight Kagome shoves Manten off his flying cloud and lots of fighting happens. Shippou uses his Crushing Top on Manten along with other things. Manten eventually gets his hands on Kagome though and starts choking her. Inuyasha notices this and throws the Tetsusaiga through Manten's spine to save her from being choked to death. That pretty much kills Manten. Hiten then takes Manten's shards and tries to avenge his dead brother.
