The pale skinned girl with long and slender limbs is Rui Fumiduki. She rarely laughs, but isn’t shy about lending a helping hand. In Akiba’s Trip she’s the first friendly face the protagonist sees after he’s attacked by the Kageyashi, a group of vampires inhabiting Akihabara.
Acquire posted a video of the rescue scene and the protagonist, an 18 year old prep school student who secretly loves to cosplay, taking a beating. He also has a younger sister in middle school, a character Acquire hasn’t revealed yet.