any-thi-ng --> anything ?

It's deliberately drawn out to match the Japanese (and presumably the way it was said).

"見えな～い～" would literally be drawn out as "caaaan't see anything". Would more natural English be "I can't seeee anything"?

> Would more natural English be "I can't seeee anything"?

Not in my opinion. I drew out the word that sounded the most natural to me in English. Other native speakers may have different opinions, of course.

P.S. May I recommend filling out a little of your profile with your language skills? Just a couple of lines can help a lot.

I think drawing out "anything" rather than "see" each imply a slightly different meaning, neither of which exactly matches the tone of emphasizing "can't see" from the Japanese, but either of which are adequate.
The reason this sentence caught my eye, though, is that "any-thi-ng" looks like an odd way to extend vowels, a form I haven't seen before. "Aaaaanything"? "Anyyythiing"?

> The reason this sentence caught my eye, though, is that
> "any-thi-ng" looks like an odd way to extend vowels, a
> form I haven't seen before. "Aaaaanything"? "Anyyythiing"?

The second. I wouldn't read too much into it - it's just a translated from a manga / web comic / game.

I decided to lose the "anything" (as it suggested to me な～にも) and lengthen the "seeeee".