BLAME!

Serial Experiments Lain.

Ergo Proxy is so mysterious that I’ve seen it twice and am still not sure what the fuck actually happens

Haibane Renmei.

As in “what the fuck is even going on here?”: Serial Experiments Lain.

I think Apothecary Diaries does a stellar job

Sonny Boy!

What’s a mysterious atmosphere?

Ergo Proxy is one that comes to mind. ‘Serial Experiments Lain’ is another good one.

Those are my ideas of mysterious.

Another

Probably .hack//SIGN but tbh the atmosphere and the music are that show’s only merits. I can’t really recommend it.

Yes, love Shadows House. It didn’t help that for the longest time you could only get the first two volumes in the west. They’re putting more out, though I’m not sure if they go beyond the two seasons yet.

Unserious answer: Ghost Stories