This is Kamui! He’s a vampire that saved Fai’s life. He’s a past life to Lelouch Lamperouge.
Kamui refuses to let Subaru give out his blood again since he gave out his blood to Seishirō. He ends up offering his blood along with Kurogane's so that Fai becomes a half-vampire, and survive until he regains his eye.
During Lelouch's reign as emperor, the sword he used is highly possibly a tribute to the divine sword of Kamui from X-1999.
Lelouch's character design is based on Kamui Shiro from X-1999 and Tsubasa Reservoir Chronicles by CLAMP who were also the character designers for Code Geass.
Lelouch's alias "Lamperouge" can mean "The Emperor" if the japanese letters are rearranged.
Putting this post here for reference. Relation ties in the clubs.
https://tsubasa.fandom.com/wiki/Kamui
