Mizu is both a Simmiror and a human being, the former of which her real body which she can only access with the help of a magic being named Yuno. In her normal form she wears a wide-brimmed hat, black with a green ribbon tied around it and a moon shaped charm affixed to it. Her face is always hidden, save for her eyes, which glow for reasons unknown, the rest of her face appearing as merely a shadow. She wears black robes, though her sleeves are silver and the edges of her outfit are green. As a human, Mizu's outfit remains primarily the same, albeit adjusted in size to compensate for her new body, however, as a human her face is visible, and also appears to have black hair.
Mizu's been known as probably the more knowledgable characters in terms of knowing people - her incredible activity across both Pop Star and the human world has led to her meeting up with quite a few people, with several of them being, similar to herself, users of the Esper Eye.
Mizu spent the early part of her life looking after a bird she found that had broken not its leg, but its skull. This bird eventually grew up to be Sora, and while Mizu continued to look after her, she was one day ambushed and was forced to flee. She then spent part of her life on the run, however, she could not entirely escape the people hunting her down and was captured one day. Her captours used her magical ability to create a half magic, half artificial golem named Yggdrasil. Mizu was sent home with a somewhat sloppy memory wipe (they weren't entirely erased, just... covered, in a sense) and eventually joined an expedition team to explore a cave and hopefully come home rich. She ran into Yggdrasil once more in the cave, which used her power to power himself. She eventually backed out, due to incredible fear.
In Lunar Phase, Mizu runs into Sora once more. The two get caught up, but by the end they decide to head their separate ways.
In the Quest for the Godhand, Mizu's Guardian Luna sends Mizu into an alternate universe to test out her new invention. The invention worked, but with an unintended side-effect - a certain feature was left turned on, camoflauging Mizu in with the surroundings by turning her human. While nobody suspected she wasn't human, Mizu continued to feel increasingly more uncomfortable in this new body until she encountered Yuno, who assists Mizu by amplifying her power enough to allow her to switch forms at will. Luna later follows Mizu into the human world and forces her to leave, even though Mizu feels that her mission is important.
In the tournament, Mizu is tricked by a possessed Mint and is captured by Tatae, who forces Mizu to hand over any information she might have on Nathan or face getting turned in to the authorities. Mizu, unwilling to comply, dares Tatae to read her mind, but Tatae finds herself incapable of doing so, as her mind was blocked by the Esper Eye.
She was recently confronted by the Steel Knight, an old ally who had warned Mizu of the incoming Bounty Hunters determined to bring Mizu in. What she was convicted for is not very clear. As a result of this and a visit from one named Rizzy, Mizu was forced to leave the premises and reluctantly joined the Guild of Noble Thieves.
Mizu possesses similar combat abilities to any Simmiror, such as the ability to conjure barriers or produce mirror images of herself. She can also create mirages and shoot heat beams from the tip of her rod. Thanks to an enchantment placed by Exuro, her rod is also capable of controlling inanimate objects, which leads to her using a giant toaster as a vehicle in Lunar Phase.
As a human, she also has a few abilities she did not have before, such as the ability to temporarily turn herself invulerable to attack for a short period of time (but prevents her from fighting), a spinning kick from above, and a flaming tornado. Her human body is weaker offensively, but a bit faster than her normal form. The opposite holds true while she isn't human.
The Faceless- Like all Simirror, her hat has the magical ability to hide her face. It's probably solar-powered.
Mirror Cracking Ugly- Nathan thinks Mizu is a vampire, and implies that she wouldn't be able to see her face in her own mirrors. Mizu says she can, though it would probably break the mirror.
Take That Me- The above statement.
Master Of Illusion- Mirage powers.
Frickin Laser Beams- Can fire out of her mirror wand.
Time Lapse- In QftGH, Mizu is two years older than she was in Lunar Phase, and has the above the power.