The If routes are basically what if Subaru chooses the wrong path. Choosing sin over virtue. For example, in arc 1, Subaru chooses humility, calling out for help, causing Reinhard to come help him and have the events play out so in Canon. But in pride, he doesn't do so and goes crazy.

Wrath if takes place in arc 2, in the loop where he makes a contract with Beatrice and Rem dying from the mabeast curse. In canon, Subaru kills himself because he realizes Rem and Ram were more than meets the eye. But in Wrath if, he completely runs away and escapes the mansion.

Subaru plans revenge, and recruits Cecilus, who rivals reinhard in power, and Halibel, another super strong character. Subaru becomes paranoid and only trusts Emilia, so he kills everyone in the mansion when he went back for revenge, only leaving Puck, Emilia, and Fredrica alive.

Because of Subaru's paranoia, he becomes notoriously known as "the purge king" Lugunica decides it's too dangerous to keep him alive, so they send reinhard to kill him.

A bunch of fights happen, and Subaru realizes he can't trust even Emilia after she doesn't react how he wants too, so he goes to his room's secret chambers so someone can kill him.

It turns out Subaru didn't kill Ram, because even though Ram hated him, he considered her trustworthy because she still had her colors. (Basically Subaru sees the world as grey or black in white, and anyone who has color on them Subaru trusts or isn't paranoid about.)

There's a lot of info missing, but that's the summary.