Besides the Nurse Sakura NPC mentioned earlier, there are of course BB and her two Alter Egos, Passion Lip and Meltlilith:
BB herself is a bit of an enigma at this point for me since I'm only at the start of Chapter 4, but she's incredibly interesting regardless. She's the apparent mastermind behind all this (though there may be more sinister forces at work, as revealed in the CCC route), and contacts our Student Council via the BB Channel:
BB herself is playful and mischievous while also being sinister and cruel. Many of the other magi she has found have been tortured for their magic circuits, and is responsible for messing with the minds of Rin, Rani, and later Jinako in such a way that their Secret Gardens must be unlocked to not only progress through the Sakura Labyrinth, but to free the girls themselves as well. Secret Gardens are not limited to these girls however, as the MC's own Servant has one, as do the Alter Egos and even BB herself.
Passion Lip is far more on the Passive side than BB. However, she is somewhat Berserker-like in nature, as she can be rather aggressive when finally provoked into anger. Her attack patterns also resemble those of someone from a Berserker class. She is rather soft spoken and, in a sense, strives for those ideals often associated with being a good housewife. She develops an obsession with the MC due to kindness shown regardless of their gender, and refers to them as her "Prince." She is often harassed by (Green) Archer, and is harassed quite a bit in general, including by Alice and Nursery Rhyme. She acts as a recycle bin of sorts, with bits of junk data being stored in her freakishly large breasts, which causes them to increase in size. In a bad ending, the MC will be turned into a cube and stored in Passion Lip's breasts for the rest of eternity (creepy huh?). In other words, Passion Lip is often docile, soft-spoken and sweet, but quite yandere, and will become quite aggressive regarding certain things revolving around the object of her obsession.
Melty, the last one, I don't know so much about yet since she's a later chapter. She has a very nice voice. She is on the more aggressive side, but has more of a cool personality as far as I can tell- in other words, less hotheaded than Passion Lip could be. Interestingly, if you play with the Archer/Fem MC pairing, she will go yandere over Archer instead of the MC, but will favor the Male MC over Archer if you are using the Archer/Male MC pairing instead.
