So I looked up the kanji (鬼滅), and the first one means demon (and has an on-yomi of KI). The second one means destroy or ruin (with an on-yomi of METSU).

Yaiba means blade or sword.

Thus..., Demon Slayer must be their translation for that. I'm not sure why they put a colon and the romaji, but...

I would've probably translated it as demon-destroying blade, but... I'm not familiar with any of those words, so...