|Japanese|| 夜吹 英士郎|
|• Professional Status•|
|Affiliation|| Seidoukan Academy|
|Previous Affiliation||Night Emit|
|• Personal Status•|
|Relative(s)|| Yabuki Bujinzai (father)|
Yabuki Eika (older sister)
|Light Novel||Asterisk Volume 1|
|Manga||Asterisk Chapter 1|
|Japanese Voice||Uchida Yuuma|
|English Voice||Max Mittelman|
Eishirou is described as being lean and a head taller than Ayato. He also has a noticeable scar on his left cheek. Under the uniform jacket of Seidoukan Academy, he wears a green hoodie and gray trousers. Eishirou has light brown hair that is almost messy in appearance.
Eishirou is very cheerful and outgoing to those around him, but can turn very serious.
During Julis and Ayato's duel, Eishirou lends Ayato his Lux to fight, though he is still unnamed and unseen, even to Eishirou. Later on, he strikes up a conversation with Ayato, telling him about Julis. At the end of their talk, Ayato returns the nondescript Lux, which both amuses and mildly impresses Eishirou.
In a dream, Claudia felt Eishirou stab her and lost strength in her body while he apologized. She recalled her memories to figure out what kind of expression he had, only to express her sorrow that he was probably smiling. As she awoke, she remarked that it had been a while since she had been killed by him, realizing that she had fallen asleep while working. Soon after, Eishirou himself called her to report on the matter she asked him to investigate. She reminded him that he should probably distance himself due to Ginga moving against her. However, he told her that he was a hikage, though Claudia didn't believe his words as they were. After cancelling the call, Claudia thought about her goal and wished for it to come sooner.
Genestellar (星脈世代): As a Genestellar, Eishirou has enhanced physical ability and an aura known as prana.
Eishirou and Ayato are good friends and roommates, with the former acting as the latter's informant (usually in exchange for food).
- Eishirou has access to a lot of classified information due to being member of the Kageboshi. His job at the First Newspaper Club disguises his other, more clandestine activities.
- According to Lester, Eishirou apparently has a girlfriend named Mikizawa Midori (水城澤 翠), who is the head of the First Newspaper Club which he is a member of. Randy had witnessed her giving Eishirou a hand knitted sweater as a Christmas present the year before.