Do I need to read Challenger first to enjoy this one?

I didn't and I like this one very much. You get the story even without challengers

Nice, thank you :)

You don't, but I strongly recommend Challengers, it's hilarious

Agreed. Especially if you love or are starting to fall in love with Isogai. Challengers has some good Isogai content, though I think he shines most in KB. He’s my favorite character in both series. ♡