Itsuki Silver Matsumoto is a Starlit Heroics character created by Flareth.
She is a 18 year old girl and was once number 8 in The Darkness Requiem.
Time In The Darkness Requiem
While in the Darkness Requiem, she posed as a man by hiding under a hood, given that there were not many females in the Darkness Requiem and she didn't want to be stereotyped.
The only mission we know of Itsuki taking was her last mission before turning to the side of good.
It was to teleport into Nintendria Castle. She got into a battle with Cassandra and the others. To end the battle, Cyndra threw her alcohol bottle and it made its way into Itsuki's mouth.
Drunken antics ensued and ended up her removing her hood, revealing that she was, in fact, female. what she didn't know was that Xerizero knew all along