Compared to most Heisei Riders, Kiva's Final Form, the Emperor Form, was introduced fairly early in the series. As the series continued, Emperor Form eventually superseded Kiva Form as Wataru's primary Rider form, with Wataru transforming directly into it. This was largely due to the fact that the base Kiva suit, and by extension all of Kiva's other forms, were too heavy to continue using as the primary suit, putting a great deal of strain on suit actor Takaiwa's body during filming. Due to this, the Emperor Form costume was created to be lighter in weight.
The suit for the base form of Kiva is known to be the most straining out of all the Heisei suits, mainly due to the uneven distribution of leg pieces, as well as the torso piece reaching from the neck to the lower back. The torso piece is made out of urethane, which leaves no real room for flexibility.
The weight of the Kiva suit is often falsely attributed to an inclusion of real iron chains on the shoulder and leg pieces, which are actually made of urethane like the rest of the suit and are made to be very light weight.
In Kamen Rider Decade: All Riders Super Spin-off, Seiji Takaiwa (The main suit actor for Kiva) predicted that the Kiva suit would be the heaviest suit, having worn all 10 main Heisei Rider suits. Kiva actually weighs less than Blade and Decade, the latter of which is revealed to be the heaviest of the first 10 Heisei Rider suits.
The main character Wataru Kurenai is the second Primary Rider (after Shin Kazamatsuri) who is explicitly shown to have a parent. Other Riders often have their parents dead or never explicitly mentioned of their whereabouts.