Mike Anders

Mike Anders is a young man from the future who operates as the heroic Kamen Rider Aquamarine. He was introduced under possession by the Greeed Neptune and operated as the villainous Kamen Rider Neptune

Mike ained the Aqua Driver and the Aqua Future Raider to fight monsters that appeared in his time, but ironically couldn't transform at first because he was afraid of water and his overall fear of being too weak to become a Rider. Receiving the Neptune Driver from the elderly James Albert, Albert believes that the Neptune Driver can help Mike overcome his timidness and fear, and grant him more power. However this proved futile, and even as Neptune, Mike couldn't win against the creatures of his time, lost, and Mike was knocked out of his transformation. Just as he was about to give up, the black hole that was created by Giru's death appears, and the Core Medals and Cell Medals from the past entered his body, resulting in a Greeed forming inside the Neptune Medals. This new Greeed develops an intense desire to fight, and Mike is almost instantly overwhelmed by the new being. With Mike's personality subdued, Kamen Rider Neptune fights in their home time period for a brief while, but after a time anomaly forms as a result of a meteor containing SOLU crashing into the ocean in the present day, the Neptune entity sees its chance and dives through, heading off to fight the Kamen Riders of the past.

It arrives in the era of Kamen Rider OOO, and easily overwhelms a small troop of Albert's soldiers, but is quickly intercepted by Ankh and Ethan Watanabe, who take some of his Cores in order to fight back. Neptune flees to recuperate. Without the extra Cores to stabilize him, Mike is gaining control. Ethan confronts the dark Rider, and suppresses the Greeed's personality, but it soon resurfaces. After Kamen Rider Neptune loses more of the Core Medals in his body to Ethan and Ankh, the Greeed splits apart with Mike, gaining his own body in the form of Kamen Rider Neptune. Mike profusely apologizes to Ethan and Ankh, telling his story to the two to Ankh's amusement. But Ethan tells him the true meaning of being a Kamen Rider, having the courage to see tomorrow no matter what it may bring. Just as the battle with Neptune seems bleak, Mike arrives on his Aqua Future Raider, and realizes that what he needed was not power, but courage, and transforms into the heroic Kamen Rider Aquamarine. He turns the tides quickly, and uses his Oceanic Break together with OOOs' Prominence Drop to finish Neptune off. He thanks OOO for all he has done for him, then leaps through the time anomaly on the Aqua Future Raider, to protect his time as a Kamen Rider.

During the final battle against Albert's forces, he returns to the present and gives Ethan the Super Core Medals. He then dashes off to aid the Seven Masked Rider Warriors in battle against the eight Inhumanoids, going up against a recreation of Greeed Kazari and destroying it with his Aqua Vortex.

Kamen Rider Aquamarine
Aquamarine, unlike Neptune, does not use Core Medals, but water as energy to transform. Through the Aqua Driver, a Driver that absorbs water from the surrounding environment to produce a substance called Manas Aqua, Mike transforms into Kamen Rider Aquamarine. Compared to to Neptune who uses brute force in most of his attacks, Aqua utilizes Tai Ch'i Quan in his fighting style. His Rider Kicks are the Oceanic Break slide kick and the Aqua Vortex flying roundhouse kick.
 * Height: 198cm
 * Weight: 80kg
 * Punching Power: 5.8 t.
 * Kicking Power: 18 t.
 * Maximum Jump Height: 80 m.
 * Maximum Running Speed: 100 m. per 5.8 sec.

Aqua Evolution
The more water Mike absorbs, the form will change. The further he transforms, he received upgraded version of his Rider kicks.

Prue Aquamarine
Pure Aquamarine is the speed form of Aquamarine. Using this form, Aquamarine's power decreased and speed increased. His Rider Kicks are the Oceanic Swift slide kick and the Aqua Tornado flying roundhouse kick.
 * Height: 198.5cm
 * Weight: 90kg
 * Punching Power: 3.5 t.
 * Kicking Power: 15 t.
 * Maximum Jump Height: 100 m.
 * Maximum Running Speed: 200 m. per 7.0 sec.

Rough Aquamarine
Rough Aquamarine is the power form of Aquamarine. It's the opposite of Pure Aquamarine form. Aquamarine's speed decreased and power increased. His Rider Kicks are the Oceanic Punish slide kick and the Aqua Berserk flying roundhouse kick.
 * Height: 199cm
 * Weight: 100kg
 * Punching Power: 10.5 t.
 * Kicking Power: 28 t.
 * Maximum Jump Height: 60 m.
 * Maximum Running Speed: 90 m. per 4.5 sec.

True Aquamarine
True Aquamarine is the most powerful and true/final form of Aquamarine. Being more powerful than Rough Aquamarine and more faster than Pure Aquamarine. His Strongest Rider Kicks are the Oceanic Climax slide kick and the Aqua Finalie flying roundhouse kick.
 * Height: 200cm
 * Weight: 105kg
 * Punching Power: 15 t.
 * Kicking Power: 36 t.
 * Maximum Jump Height: 120 m.
 * Maximum Running Speed: 120 m. per 10.0 sec.

Kamen Rider Neptune

 * Height: 204cm
 * Weight: 89kg
 * Punching Power: 3.5 t.
 * Kicking Power: 7 t.
 * Maximum Jump Height: 45 m.
 * Maximum Running Speed: 100 m. per 6.1 sec.

Similar to OOO, Mike puts three Core Medals on the Neptune Driver, and transforms into the evil Kamen Rider Neptune. The chest design has an inverse triangular position, which is arranged in the order of the Shark on the right, Whale on the left, and Wolffish below the Shark and, unlike OOO's vertical (on his chest) and diagonal (on his Driver) arrangement. Kamen Rider Neptune is designed with the light blue Shark Head, the dark blue Whale Arms with a whale's head on right shoulder and whale's tail on the left shoulder, and the dark red Wolffish's legs. Kamen Rider Poseidon uses an extended spear, the Deepest Harpoon as his weapon.

Kamen Rider Neptune is actually a Greeed inside Mike's body. The Greeed overtook Mike's body and arrived in the present. It has the ability to create Waste Yummy, similar to how Uva did. The Greeed split from Mike, after losing some Core Medals to Ethan and Ankh. He was able to form his own body using Core Medals and Cell Medals, in the form of Kamen Rider Neptune. Soon after, Neptune was defeated at the hands of Kamen Rider OOO Blaze Combo's Prominence Drop and Kamen Rider Aqua's Oceanic Break.

Aquamarine

 * Aqua Driver: Aquamarine's Transformation belt
 * Aqua Future Raider: Aquamarine's Rider Machine

Neptune

 * Neptune Driver: Neptune's Transformation belt
 * O Medals: Transformation device
 * Deepest Harpoon: Neptune's Personal weapon