Shingeki no Kyojin, Houseki no Kuni (TV) Recommendations
They're both set in a distant future with naive main characters that simply want to know more about the world they live in. The overarching themes that come later in the series are similar too, at least in my opinion.
Both shows present very interesting settings, and part of the fun is just learning about the world and its mysteries.
I would rather not spoil all of Attack on Titan but these shows can be strikingly similar when looked at closely. The enemies in Attack on Titan (the the titans) hold an unusual likeness to Houseki no Kuni's Lunarians. While at the same time both shows display similar themes of wanting to change, grow stronger, etc. Both protagonists seek out the truth of the unusual circumstances they live in.