No.6, Karneval (TV) Recommendations
Both series take place in a futuristic future society. There are supernatural phenomenons and mysteries. Both main characters are fugitive criminals. A secret society/organization is after them.
They have black haired and white haired protagonists, they both deal with some sort of government making experiments and the white haired protagonist is looking for someone very meaningful to them while the black haired protagonist helps them find that person throughout the story.
-Both are great (in my opinion) underrated shows
-No.6 has a shounen ai canon relationship while Karneval just has the vibes
-Both have two characters going on "adventures" to save something
Even though I described them terribly, I highly recommend watching both even if you're not into that shounen ai kind of thing. These are probably two of my favorite animes. Hope you enjoy them as much as I did.