RE : Who is Chi ?

Why ChrNo ?

As ChrNo said, the nickname is from Chrno Crusade, but it's not the only meaning.

ChrNo is a gentle demon which lives with a nun, Rosette Christopher, in New York, around 1930. Those two are more than just friends, they are connected with a "clock", more like a Life-time-machine. Thanks to that clock, Chrno can change into a powerful and dangerous demon, like Chrno used to be, to help Rosette fighting other evil demons. When this happens, Rosette's life-time decreases.

In this story, Time is the important key.

As a japanese manga, Chrno must be a Engrish word of the English word Chrono

Now about ChrNo, it can be cut into 2 words : Chr and No
so you can read two abbreviations Christian and Nott which is the name of the main character from Jen's first Manga.

Back to chrono : Trépa has made the pun once : chrono post ! referring to ChrNo's post in jphip and a french company, which is we can say it, a lame pun :p