Now that Sora finds himself in a world where he feels he belongs, and moreover, feels like he’s the best (and hasn’t yet been proven otherwise), of course he’s going to crash Kurami Zell’s coronation. Zell accepts his challenge, which means she gets to pick the game they’ll play to decide who rules Elkia. This results in Sora and Shiro’s toughest challenger yet, quite a step up from the flustered Dora, who’s still wrapped in a sheet for some reason. Change your clothes, girl!
Not only do they get a tough challenger in Zell, who selects a game of chess that turns out not to be chess at all (more on that in a bit), they also figure out that Zell rose to the top with outside help. Humans being at a tremendous magic disadvantage in Disboard (where Elkia is dwarfed by all the other countries), Zell, ostensibly looking out for her people, decided to hitch her wagon to the Elves, the most powerful of the rival nations. When she officially comes clean with this and states her case, it makes a lot of sense, both to Dora and to me.
But standing by and let Zell be a puppet king for the Elves (even if she says she won’t be one) isn’t Sora’s style. He doesn’t think Zell, someone who relied on cheating through the magic power of the Elves, deserves to say whether humans can’t survive without subjugating themselves, and she certainly doesn’t deserve to rule if she blabbed all this to Sora and Shiro, when for all she knows they’re also being backed by an outside country. Sora thinks humans are being sorely underestimated, and they’re going to do something to remedy that.
In a standard game of chess where the pieces move how they should without hesitation, Shiro is unbeatable, but here it isn’t the pieces you move, but their wills. and Shiro is frustrated to tears. If Shiro were a single player, it would be over, but Zell is playing Blank, a two-player team, and Shiro’s difficulties help her brother determine the true nature of the game they’re playing, and the path to victory. The pieces are basically now literal soldiers in literal armies commanded by Zell and Sora, and whoever is the strongest and most inspiring leader is going to win.
When Zell cheats again by brainwashing Sora’s pieces into defecting, Sora counters by flipping Zell’s queen with his dating sim skills. It’s all very stirring and fun, if a bit ridiculous. The battle isn’t over yet, but things aren’t looking good for Zell, which is good for Imanity. And she has yet to learn Sora and Shiro aren’t being backed by anyone; if she did, she might have already conceded that it’s too early for humans to be throwing in the towel and accepting protection from the Elves.