slimes dun have genders and i think anyone can be called-chan at some point it depends
In most manga/novels I read slimes are genderless, but if they are intelligent, they decide on which "gender" they are (not biological) and here we see sui is male since MC keeps complimenting him that he is a good boy. Also about -kun and -chan, in manga (anime we usually see guys with -kun and girl with -chan, but you see guys in anime being caled -chan and not liking being called it, usually that was a nickname they got in childhood or from family and they want to get read about it when they get older. The way Animeman (YouTube that is half Japanese) explained it is that although usually -chain is for girls and -kun for boys it is not a defined by gender but more like if someone is cute he or she can be -chan and girl can also be -kun, for example is she more cool than cute. There is no clear definition or separation, more personality type I think. Hope I was helpful and didn't just confuse you more. Have a great dayヾ(❀╹◡╹)ﾉ~
I'm still confused to this day. Sui is a boy, right? Why is he Sui-chan? Is he a she? Or is there no gender when it comes to slimes?