Looking for an anime I watched in the early-late 2010s, however it might have been released earlier. Please help?

So basically, the plot was about this high school(?) guy that got involved in some fantasy action due to some older man. One of the antagonists wore mostly black(?) and he was immortal, and apparently couldn’t taste anything from what I remember.

On the final episode of the anime I believe, the protagonist and this antagonist (or perhaps anti-hero) become friends, and in the end they were shown knitting. And in another scene, they were eating cake. Because even if this antagonist couldn’t taste anything, he could smell them. I think that the antagonist was actually going to die in a few days or weeks, so they were just enjoying their last few moments while he was still alive.

I vaguely remember a sword being involved, though I can easily be wrong. Does anybody know what anime this might be?

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