Don't worry, you don't need permission! The whole reason why fanfic exists is because it's a nonprofit organization organization that doesn't make money off other people's work. I wrote several fanfics from manga, one of which is the first of its kind since it's one of those elusive manga nobody really knows and didn't have to ask permission.
As long as you're not making money say for example, making merchandise of it, selling it online, or calling it your own, then you should be fine. Sometimes, fanfic writers will put up some kind of disclaimer in the beginning of their stories saying something like "I do not own any of the characters, or manga since they're not my own blah blah blah" something like that. Good luck!
Thank you so much here i was like 'what if that counts as stealing' so i'm super relieved.
Hey I was thinking about writing a fanfic about a manga from here but how can i get permission i mean it would be stealing if dont right? What should i do? Also i will say that it's fanfic version of that manga. Should i talk to mangaka and how can i talk to her?