Haru Kusao is a meek new first-year student at Amanogawa High School who receives a Zodiarts Switch from Libra and becomes the Musca Zodiarts . The reason why he wanted the Switch was to protect his (for a long time, only) friend Ran.
She had long sworn to protect him, after an incident where upperclassmen at their previous school threw Haru's friendship charm with Ran's name on it into the pool and teased him, but she stood up for him and retrieved the charm, thus gaining a disdain for upperclassmen. However he had gotten a high off the switch, and still saw Ran trying to protect him (as both himself and the Musca Zodiarts), leading to an increasingly unstable mental state
However, his power to convert his body into a swarm of flies was negated when Fourze used the power of the Net Switch onto Musca, forcing the Zodiarts to stay solid while Fourze assumed Magnet States. However, Kengo warned that if Haru's Zodiarts form was destroyed while he was mentally unstable, he would remain that way. Just then, Ran yelled to Haru an apology for trying to protect him when he didn't want protecting. Haru's heart was reopened, and he asked Gentaro to send him back to his body, and was blasted away by a Super Electromagnetic Bomber.
Later, after returning to his body, Haru is given provisional membership alongside Ran while recuperating from his injuries in the hospital. However, poor Haru was used by Leo to bring out Ran, who was the last Horoscopes, Pisces. By the end of the series, Haru and Ran become official members of the renamed Space Kamen Rider Club.
In the movie Kamen Rider Fourze the Movie: Everyone, Space is Here!, he used the Net Switch as a relay to help create the Fusion Switch.
Musca Zodiarts (Infinite Monster Plant)
A second Musca Zodiarts, already evolved to its final stage, is created by the Akumaizer's Infinite Monster Plant in Kamen Rider × Kamen Rider Wizard & Fourze: Movie War Ultimatum. It fights against Kamen Rider W, but is easily destroyed with a standard flying kick.
Super Hero Taisen Z
The Musca Zodiarts is one of the revived monsters that join Space Shocker, but it's seemingly defeated once again. It's seen for the last time fighting against the Super Sentai team Flashman.
Musca Zodiarts Form
- It can spit a sticky mucus-like slime from its mouth and can jump high, this form known retroactively as "Phase 1".
- The Zodiarts reacts to Haru's emotions and desire to become stronger and undergoes a metamorphosis that gives him neon green armoring on his forearms and shins that increase Musca's physical power [this form being known as "Phase 2"], though that was proven no more then decorative to the more adept Kamen Riders.
However, Musca soon gained the ability to convert his body into a massive swarm of flies when fighting Fourze in Elek States, though he couldn't control himself while doing so.
- Once Haru hit the Last One phase, Musca had turned into a terror that is "Phase 3". On top of his previous abilities, Musca gained better and spiked armor, allowing him to withstand more punishment. It also gained wings, allowing Musca to fly, and the projectile slime turn into rainbow-hued slime balls that explode upon impact.
However, his power to convert his body into a swarm of flies was negated when Fourze used the power of the Net Switch onto Musca, forcing the Zodiarts to stay solid while Fourze assumed Magnet States.