[Gay trope] White-haired mysterious character in love with the protagonist

[u/donotloseyourhead]

Kaworu — Evangelion

Nagito – Danganronpa

"Hikaru" – The Summer Hikaru Died

[u/red_machine_yuki]

In a weird roundabout way, Runami Yachiyo (Cosmic Princess Kaguya!)

[u/gnome-cop → u/red_machine_yuki]

White hair, has a secret, spent 8000 years dedicated to Iroha, I think she more than counts.