Sakuya Izayoi is the head maid of the Scarlet Devil Mansion and the mistress's main bodyguard. She takes care of Remilia, Patchouli, and Flandre. She also keeps an eye on Meiling and the fairy maids.

Sakuya is performing her usual maid duties when someone screams "Thief!" from the library. She dashes off to capture the perpetrator, already thinking of a harsh reprimand for Meiling for letting someone sneak in...

Sakuya stops time to capture the thief (i.e., Marisa) as she is trying to run away. The maid takes back the stolen books and prepares a shower of silver knives for the culprit. When she lets time flow again, the only thing the thief can do is focus on dodging the knives.

After Sakuya gets rid of the rat (i.e., the thief) and finishes reprimanding the gatekeeper for letting her in, she returns to her regular duties. Uninvited guests can never sneak in under her watch. You could call her the final barrier of the mansion.

Sakuya's destiny changed a lot for the better after she met Remilia. She had always been skilled, but now she has risen to the position of head maid and become the close associate of a vampire. The relationship goes both ways though―Remilia must put a lot of faith in Sakuya too.