A Honkai Impact 3rd and Benghuai Xueyuan character. The second Herrscher after Welt Joyce, and dominated the power of the void. She became a Herrscher and started the Second Impact in 2000 at a Schicksal laboratory and has pulled the whole North Siberia into her void realm. Rumours say that she was inhumanely experimented on and tortured by the tests and therefore awakened the Herrscher consciousness inside of her and took the girl's mind.
Sirin perished together with S-rank Valkyrja Cecilia Schariac and four other A-rank Valkyries (Squad Snow Wolf) in a series of nuclear explosions caused by a rain of missiles from Schicksal.
After Sirin's death, her Herrscher core got been divided into five parts, those being the main Core of Void itself and the 4 extra Authorities granted to her, those being the Gem of Conquest (Thunder), Gem of Desire (Wind), Gem of Haste (Fire), and Gem of Serenity (Death). The four different Gems are kept separately by Schicksal and Anti-Entropy, while the Void Core was secretly obtained by Otto while everyone else was unaware of its existance.
In the current game era (Honkai Impact 3rd) Otto Apocalypse created K-423 (a clone of Kiana Kaslana mixed with Sirin's DNA) using the techniques he used for his adopted granddaughter Theresa Apocalypse, and inserted the Void Core into the empty clone, succesfully giving it life and Sirin a new body.
Sirin's soul/consciousness within the core then split into two: the side that wanted a happy life as Cecilia's daughter (K-423 Kiana), and the side that wanted revenge on the world (Void Kiana).
Thus was Sirin the Herrscher of the Void resurrected/reincarnated, just as Otto secretly planned. The Void's power doesn't normally show up, but in some special conditions, her power would burst dealing a large scale of destruction. The mysterious sound in Kiana's (K-423) head is actually Void Kiana's, her other self, but she doesn't have a clue.
She is named after the Russian mythological creature of the same name which is usually depicted as a beautiful half-woman, half-bird.
In version 5.0, an ELF form of her was released. In version 6.9, Miracle Magical Girl, a Magical Girl version of Sirin from a bubble world, became playable as a Mecha/Fire battlesuit.