- "Sorry, but I'm not in the mood to fight you now."
- ―Thetis to Grey, Mega Man ZX Advent
Thetis (テティス Tetisu, lit. "Tethys") is a character from Mega Man ZX Advent. He is a kind boy that loves swimming and the sea life, 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.
Model L grants Thetis many superhuman abilities, such as swimming at super speed, ice manipulation, and the ability to breathe underwater.
Thetis appears as a young boy with short blue hair styled into the infamous "ahoge" (literally translating to 'stupid hair'). He is characterized by his innocent, vibrant expression. He wears his Mega Man jacket right under his Mega Man-inspired hoodie and also sports a pair of shorts. He also has a red triangle on his forehead, confirming his status as a Reploid.
He's a kind person who appears to be quite upstanding. He loves the ocean and sea life. Beneath this exterior is an extremist however. He harbors animosity and hatred against mankind, participating in the Game of Destiny in order to gain the power to kill all humans and restore the earth to its pure state.
Mega Man ZX Advent
The player encounters him again at the Highway where he is attacking citizens to feed Model W. He Megamerges and jumps into the ocean with Grey/Ashe following him. He explains that he is participating in the Game of Destiny to punish humans for polluting the sea. After he is defeated, he retreats and takes the Model W with him. He appears briefly after Grey/Ashe breaks Aeolus's cipher with all the other Mega Men.
He also appears after the defeat of the eight Pseudoroids in Ouroboros 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 defeating Albert, Ouroboros starts collapsing. Model Z separates from Vent/Aile in order to keep Thetis and the other Mega Men busy by freezing the Biometals, which in turn freezes the four Mega Men. Their fates are unknown, but if the game is cleared on Hard Mode, all the Mega Men are seen alive and well 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 thinks happened to the data, the four show up.
- The battlefield is the ocean, reminiscent of Fairy Leviathan's battlefield in the Mega Man Zero series.
- He dash-swims around the screen and twirls the halberd around. Sometimes he feints this attack.
- He stops and fires off a triangular wave of energy not unlike Childre Inarabitta.
- His charged attack differs depending on which character is being used. As Grey, he fires off a pair of ice dragons that home in on him. As Ashe, he manifests a thick, spiky ice formation which he then shatters, releasing a series of ice shards. These attacks can be countered using a fire attack or the Homing Lasers.
- His ultimate attack involves him summoning a machine from underground that shoots out several snowflakes, and then proceeds to create a vacuum that sucks in all nearby, the snowflakes themselves having been dispersed about from the force. They can be destroyed before the vacuum effect occurs using the Homing Lasers.
- Thetis appears to be the only Mega Man in ZX Advent who wishes to think about peace. This may indicate that he is actually a good character, but was possibly corrupted by Model W. He is also the only enemy that appears to want to appeal to the player, with all other enemies indicating annoyance at their "failure to understand" or feeling that nobody else would "understand the glory of our plans".
- For unknown reasons, Grey refers to Thetis as a human, even though he is a Reploid. 
- ↑ Thetis: It's too bad... I thought you, at least, would understand what I'm trying to accomplish! I won't give up. I shall awaken Model W and change this world for the better!
- ↑ Grey: So you take innocent lives!? You kill humans just like yourself.
|Mega Man ZX series|
| Vent • Aile • Ashe • Grey • Girouette • Prairie • Guardians • Hunters • Raiders|
Sage Trinity • Aeolus • Atlas • Thetis • Siarnaq • Serpent • Prometheus • Pandora • Pseudoroids
|Mega Man ZX • Mega Man ZX Advent • Legacy Collection|
|ZX (Vent's story) • ZX (Aile's story) • ZXA (Grey's story) • ZXA (Ashe's story)|
| Biometal • Game of Destiny • Humanoid • Locations • Mega Man |
Mega Man ZX (manga) • ZX Tunes • ZXA Tunes • Rockman ZX Soundsketch - ZX GIGAMIX