Voltron: Legendary Defender

The web-television reboot of GoLion and Voltron: Defenders of the Universe follows the adventures of the pilots of five robot lions who can combine to form Voltron (and their friends) who defend the universe from peril.

In season 2 episode "The Depths", Hunk and Lance of the Yellow and Blue Lions end up crashing into the ocean of an unfamiliar planet. There, they encounter the merfolk of a small village who are lead by Queen Luxia. The merfolk welcome Lance and Hulk warmly... Perhaps a little too warmly? There's something suspicious going on with the merfolk, who seem to want to keep the two humans there forever.