Thetis

Thetis is a character from Mega Man ZX Advent. He is a kind boy that loves swimming and the sealife, but he wants to punish and rid people from the world for dumping their waste into the sea. He is the chosen one for Model L, the Ice Mega Man. The player battles him at the Highway.

Personality
He's a kind person who appears to be an upstanding person. He loves the ocean and sealife. However he has a nasty side as well. He hates humans for polluting the sea and plays the Game of Destiny to punish them.

Mega Man ZX Advent
The player encounter him at the Arctic Ice Floe with Atlas. Instead of fighting you, he flees leaving you to fight Chronoforce.

The player encounter him again at the Highway where he is attacking citizens to feed Model W. He Megamerges and jumps into the ocean with you following him. He explains that he is participating in the Game of Destiny to punish humans for polluting the sea. Then you battle him and defeat him. He retreats and takes the Model W with him. He appears briefly after you break Aeolus's cipher with all the other Mega Men. He also appears after the defeat of the eight Pseudoroids in Ouroborous with Atlas, Aeolus, and Siarnaq. They are about to attack Grey/Ashe when Vent/Aile arrive and fights them instead, allowing the player to continue. After defeat of Albert, Ouroborous starts collapsing. Model Z seperates from Vent/Aile in order to keep Thetis and the other Mega Men busy. Model Z freezes their Biometal which freezes them. Their fates are unknown, but if the game is cleared in Hard Mode, you can see all the Mega Men well and alive in their Megamerged forms. (It's also implied that the original immortal Reploid Data was inserted into them, as, right after Master Thomas asked Master Mikhail what he think happened to the original immortal Reploid data, they showed up).

Attacks
When you fight him, you're in the ocean, reminiscent of Leviathan's battlefield in the Mega Man Zero series. He dash-swims in the screen, attacks and then swim-dashes out of the screen. He sometimes uses the spinning halberd attack or the triangular ice projectile. When playing with Grey, he'll fires an ice dragons like Leviathan's. With Ashe, he'll create a chunk of ice and shatter it, causing the fragments to fly in different directions. He will also summon ice flower cannon to fires some current at the player. Then he will create a tornado of snowflakes, also like Leviathan except that snowflakes is homing spears.

Human or Reploid?
Thetis is somewhat of a controversial character, as his species is contradicted. The fact that he has a upside down red triangle birthmark on his forehead would imply that he is a Reploid. However, in Grey's storyline, Grey explicitly refers to Thetis as a Human.