[Baltan II]

Ultraman Nexus is about a young man recruited into a secret organization to fight unknown deadly monsters, and the strange giant that seems to be protecting humanity from the threat as well.

Kamen Rider Black is about a young man whose humanity and stepbrother are taken from him by an ancient organization looking to advance human evolution under their rule, who rebels and now fights against the cult's minions.

Black's plot takes a very standard and straightforward approach as its plot is very similar to most every Showa Kamen Rider series. Nexus differs a little bit in that a) its universe is typically fully aware of the monsters threatening humanity and b) the main character is not merely the titular hero's alter ego or host.