[@KrischKrisch] Color-wise, I don't think it'll be a problem. At least there isn't any foreseeable ones on my part.

As for the image, not sure if you wanted someone who looked liked gambit or someone who playfully dabbles with cards. If you're interested, some alternative images: [url=https://s1.zerochan.net/Gambit.600.386826.jpg]1[/url], [url=https://safebooru.org//images/592/e184369957659d26f5aa4894802d9bacc1f56721.jpg?594636]2[/url], [url=https://safebooru.org//images/391/6f09a0350169b3a84433954761047fc32b121b67.jpg?391017]3[/url], [url=https://safebooru.org//images/343/4bcd379fff462583d9f2102655cc90841f32cfd2.jpeg?343100]4[/url]

Devil Fruit is fine. Initially I was worried that it was just purely for stat boosting, but the Spade Spears made it more befitting of One Piece.

Also, since turning on Spade Surge is a prerequisite to use Spade Spears, it'll look like this.

[color=ed1c24]Suit-Style: Spade Surge:[/color] House activates another sutsu-power to increase his speed and reaction times, enabling him to use the [color=ed1c24]Spade Spears.[/color]
[INDENT][color=ed1c24]Suit-Style: Spade Spears:[/color] House's hands transform into a black spade shape, making them extremely sharp and durable, effectively turning his arms into thrusting weapons. The stem of the spade protects about half of his lower arm from damage as well.[/INDENT]
Yeah, and like I mentioned in the OP, we always round down when it comes to Willpower.

Lastly, although the fruit grants stat boosts, even if you described it as "doubling them and turning his pupils into diamonds", stat-wise, it would translate to that exactly. I'll think of a fair value for now.

Massive increases would be considered different skills and not just a technique. Examples would be Luffy's Gears or the Mink Tribe's Sulong Form.

Otherwise, everything else seems fine.