大東亜聖戦之初
Dai-tōa seisen no hatsu
"Dai Tōa seisen" means the great war in the Greater East Asia (aka Pacific War, aka WW2).
I'm not sure about the last kanji. It appears to be 初, which means beginning or first, but that doesn't make grammatical sense. I mean, it could plausibly mean that the sword was made at the outset of WW2, but that's not really how the syntax, word choice, or the grammar works. Anyway, it appears to be an inscription from WW2 - or a fake inscription that is trying to get passed off as a WW2 inscription.