Girl Haven GN

Three years ago, Ash's mom, Kristin, left home and never came back. Now, Ash lives in the house where Kristin grew up. All of her things are there. Her old room, her old clothes, and the shed where she spent her childhood creating a fantasy world called Koretris.

Ash knows all about Koretris: how it's a haven for girls, with no men or boys allowed, and filled with fanciful landscapes and creatures. When Ash's friends decide to try going to Koretris using one of Kristin's spell books, Ash doesn't think anything will happen. But the spell works, and Ash discovers that the world Kristin created is actually a real place with real inhabitants and very real danger.

But if Koretris is real, why is Ash there? Everyone has always called Ash a boy. Ash uses he/him pronouns. Shouldn't the spell have kept Ash out? And what does it mean if it let Ash in?