
Ok I did some research too. I read the raws and the MC actually uses the katakana スイ(Sui), so no kanji at all. Actually the kanji you wrote (酸い su+i, it's an adjective) is the one for acid, but in matters of taste, so acid or sour taste. It would also sound really strange to give it an adjective as a name probably.
Because of this, I actually think that my random guess was actually right, I'm so happy ε=ε=(ノ≧∇≦)ノ
Anyway, you actually made me curious about Suicune and i also looked that up. Sadly I couldn't really find anything. The part of Sui is probably the one that means water (it's a water type god, so it would make sense) but for Kun, I have no idea. Maybe it sounded interesting, I don't know ╮( ̄▽ ̄)╭

Cool. It's always fun to research other countries languages. But everything non-Roman languages is hard to decipher for me especially when it can have readings then 1 and more different types it been used haha. (Which make studying Japanese by myself harder.)
If we don't know what form has been used originally then it could go both ways ٩(๑❛ᴗ❛๑)۶
But it's always fun and interesting to know. (=・ω・=)
Sui already cute even w/o that name.
BTW is Sui a girl or a boy. Someone told me before that in the novel Sui is a girl, but here it's always said "he" ( ̄∇ ̄") So confusing if Japanese speaks genderless

Like you said, it's genderless. I mean, a slime is not a thing that has gender, so the name also doesn't have one.
Regarding the name you said, you should try and look up the kanji. Even though they could have the same sound it doesn't mean that it's the same one. When it comes to Japanese names, they don't have a specific gender in it, like the western ones, they are just used more by some people for different genders. They just look at the meaning usually

Unfortunately so true. But I don't have the money to study for it. Nor really the time to really go for it. So for now only basics. Although can understand some of Anime w/o sub or listening to Japanese audio/cd drama I can sort of know what's going on.
( ̄∇ ̄") But I don't think they gonna use those words IRL, after all must watch out not to speak rudely when speaking to a native Japanese!
@.@ so many things to think and watch out for. G'luck in your studies!
I wish my dad was still alive then he could have teach me, (I'm actually halve Japanese on my fathers side), but he passed away when I was little. I grew up in the West when my mum married with a Westerner. (I can't even speak my mom's language)
Did he just name a slime "water"? (≧∀≦)