I assume she had a lover a long long time ago and actually managed to stay with em til he died of old age. Hence why she seems to know a lot about what's happening to main girl. That or she just reads and researches a lot of stuff
For those that want to know about the sensei's backstory, have a read of the of the authors other story
Heal & Squeeze which can be found here: https://mangadex.org/title/92350fa6-2b08-48fc-9dc3-2591c30646a8/heal-squeeze
A lot of the characters are the same and it can be thought of an alternative universe perhaps; its a rather good short manga what's really worth a read if you like this or the authors other series.
Basically in that story the sensei's backstory is that she fell in love with the a guy and stayed with him until he passed away, whilst still drinking blood from him in his old age. However due to his fragile body she would use a sterilised blood iv, as her teeth damage his sensitive skin too much and his old body wouldn't be able to fight off an infection.
For those that want to know about the sensei's backstory, have a read of the of the authors other story
Heal & Squeeze which can be found here: https://mangadex.org/title/92350fa6-2b08-48fc-9dc3-2591c30646a8/heal-squeeze
A lot of the characters are the same and it can be thought of an alternative universe perhaps; its a rather good short manga what's really worth a read if you like this or the authors other series.
Basically in that story the sensei's backstory is that she fell in love with the a guy and stayed with him until he passed away, whilst still drinking blood from him in his old age. However due to his fragile body she would use a sterilised blood iv, as her teeth damage his sensitive skin too much and his old body wouldn't be able to fight off an infection.
Either Heal and Squeeze is an alternate story or it's the same universe set in the past since Sakura talks about how vampires are being divided due to elitization which is shown in Please Give Me Your Blood
Though Sakura feels like a proto Sumire.. maybe we'll get to see her as well? Kikyo, Dahlia and Mimosa already showed up anyway lel maybe Sakura has ties with Sumire or something