(Welcome. You’re in Spoiler City) I had no internal debate about this one, because this death always, and I mean always makes me cry. It was so sad that merely hearing music associated with it makes me cry.
The main character, Teito Klein’s, absolute best and only friend is Mikage Celestine. They are Zaiphon users who were training their abilities in the Barsburg Military Academy to become soldiers. Teito is a former sklave (basically a slave) who has lost his childhood memories. He is captured by the Barsburg Empire and sent to the academy to become a soldier due to his great talent.
Teito isn’t very sociable, and he comes off as cold because of how he’s been treated throughout life, but the outgoing, gentle, lovable and just all around great guy Mikage eventually becomes best friends with Teito.
Despite his dislike of violence, he dreams of being a soldier so that he can protect his family, but he willfully gives up this dream to help Teito escape after he’s charged with treason by the church.
He’s tortured for information and even his family is threatened with death if he does not tell them where Teito is. He escapes as a one-winged Kor, which is basically a failed attempt at trying to possess someone with the Ghost ability. In this case, the main baddie of the show, Ayanami, tried to possess Mikage with it.
Once a person is turned into a one-winged Kor, there is no saving them and reverting them back to normal like you can with a full-fledged Kor. If left alone, the one-winged Kor will eventually consume the soul of the person being possessed. The only way to save their soul is to kill the Kor and the person being possessed.
Mikage faces Teito and Frau, a bishop at the church that Teito flees to and one of the titular 07 Ghosts, Zehel, and eventually sacrifices himself on Frau’s scythe.
Teito is crushed by this, and dammit so was I. He deeply mourns for quite some time until Frau finds a little baby Fyulong and reveals that Mikage was reincarnated into that baby Fyulong who wishes for nothing more than to be by Teito’s side forever and protect him, even if he can’t remember who he used to be.
I have never blubbered my eyes out for so long at a show, and it made it so I can’t hear several songs on the 07 Ghost soundtrack (which is incredible, btw) without at least wanting to cry. Especially Tree’s Filtered Sunlight and Be Pure, My Child and Sleep.

The bond between these two and their loyalty to each other was just so amazing to watch and it pains me that we didn’t get to see more of Mikage because he truly was an awesome character that you’d just love to know in real life.
The only thing that keeps me from crying when looking at Burupya is…..dammit, he’s so cute! Look at his wittle ears and his tiny scar!
You’re the best emotional brain bleach ever, Burupya!
Honorable Mentions (still spoilers): Toboe from Wolf’s Rain, Wolfwood from Trigun, Hughes from FMA.