I spent almost an hour reading the whole series up to the half of chapter 14 I would rate this a solid 9/10 Manga even if it really doesn't seem like an Isekai at all. The MC is some regular dude who crew up as a Blacksmith and somehow obtained skills to craft a Katana from the modern world? The magical twist is how the blade came out to be cursed? Storywise, it's sort of advanced, prioritizing the effects of the MC's sword throughout people. The examples of swordsmanship love may be a bit extreme, yet it's very fitting which suits of how other worldly a Katanais here. I do enjoy how this series does not pull it's punches when displaying the true power of this sword