Suggest me a underrated 10/10 anime

I've watched almost all popular animes as I've been watching for more than 6 years regularly. Like if an anime is bit popular in that year, I've watched it. I want to watch something which you think I haven't watched and isn't popular but is great anime.

Like I've recently watched Kenichi The mightiest disciple and liked it. Underrated animes like that.