ジ (U+30B8) is turned into "zo"

[Sainan]

It should be "ji" for the closest phonetic match, tho sometimes it's also transliterated as "zi".

I would PR myself, but I could not understand the project structure.

[Tatsh]

Not seeing this as it now outputs zi.

Yes it should be ji as in Hepburn but the form used in Unicode data is systematic conversion of s->z when " is added, as with (t->d, ts->dz, t (ch) -> d (dh I guess)).

If you want more close Japanese transliteration, try Kakasi. There is a new Rust version that properly handles Unicode: https://github.com/Theta-Dev/kakasi