Kisaragi Yuu

Kisaragi Yuu, created by Phineasmon302, is one of Kise Yayoi's three future children with Kisaragi Gentaro, the main character of Kamen Rider Fourze. He and his twin brother Jou are able to become the two-in-one Kamen Rider Twize (仮面ライダートワイゼ Kamen Raidā Towaize).

Personality
As the oldest child of the family, he feels like it's responsibility to keep his siblings out of trouble, most of all when his twin is a reckless adrenaline junkie and their two-year-old sister is curious by nature. Partially named after his late grandfather Yuuichi Kise, he values his family above all else, but also inherited his father's willingness to make friends, which can sometimes get the best of him. He also has, at least for his age, a surprising knack for mechanics, and is often helping out at Kisaragi Motorcycle Engineering; in fact, he was the one who came up with the design of Kamen Rider Twize's RiderMachine, the Machine Jankenper. He's also trying to start an Enka Appreciation Club, but still hasn't managed to make that idea take off.

Relationships
Kisaragi Jou - Twin brother.

Kisaragi Nadeshiko - Younger sister.

Minamoto Kazuki - Childhood friend, in virtue of the friendship and professional partnership between both of their mothers.

Minamoto Emiri - Childhood acquaintance, in virtue of the friendship and professional partnership between both of their mothers, and eventual ally.

Hino Madeleine Taylor - Childhood friend, in virtue of the friendship of both of their mothers, and ally.

Aoki Hyouka - Childhood friend, in virtue of the friendship of both of their mothers, and ally.

Matsubara Ringo - Close friend and ally.

Amagasaki Yusura - Classmate and ally.

Kurei Neyumi - Classmate and ally.

Kamen Rider Twize
Kamen Rider Twize (仮面ライダートワイゼ Kamen Raidā Towaize) is the combined transformed alter ego of both of the Kisaragi twins, with Yuu providing the 'mind'. His arsenal was developed by Philip and Utahoshi Kengo as a combination of Kamen Riders Double and Fourze's powers. His transformation belt, the Twize Charge Driver, resembles and works in a similar way to the Fourze Driver, but has two Switch Sockets rather than four; as such, Twize cannot use any other additional Astroswitch combinations or forms, relying simply on his fighting skills and lightning-based powers. Like Fourze's, though, Twize's suit doubles as a space suit, and includes a hover pack.

Kamen Rider Twize is a loyal ally to the next generation of Smile Pretty Cure, and occasionally steps up to help them out in battle, although mostly allowing them to finish the job themselves.

Etymology
Kisaragi (如月): The old Japanese name for the month of February.

Yuu (友, written as ゆう): An unisex Japanese name that can have several different meanings, the intended being "friend, companion" or "fraternity"; combining the twins' names results in Yūjō (友情), which is Japanese for "friendship".

Kamen Rider Twize's name is a pun on the word "twice", alluding his two-in-one nature.

Trivia

 * The creator's idea of pairing Gentaro and Yayoi came from various Pixiv fanarts portraying Yayoi as a Tokusatsu fangirl and, as such, having her interact with Tokusatsu characters, including Kamen Rider Fourze ones (as the second half of Fourze was airing alongside the first half of Smile), and was cemented with a picture posted by Tomimori Justin (Daimonji Shun's actor) on an entry of his blog.