The Aishi Family comes from a very long line of yanderes. Most women in Yandere-chan's family desire giving birth at a young age, such as 19. It has also been a family tradition for several centuries that when an Aishi woman marries a man, the man adopts the wife's surname. All Aishi women are emotionless until they find the person who can make them experience feelings. It is likely that there are no male yanderes in the family and the family line has consisted of female-only yanderes for centuries.
There will always be slight differences between each yandere born into the Aishi family, but never in terms of strength. All of the Aishis look almost identical to one another. YandereDev imagines all of Yandere-chan's ancestors with the same exact hairstyle, even if it feels goofy to him. The Aishi family members aren't very close. Once a yandere has found a partner, they tend to distance themselves from the family. It's likely that Yandere-chan hasn't met most of her relatives, although no one is on bad terms. While male children are unlikely, they would look similar to Senpai and would be yandere as the females are.
Relationship between an Aishi woman and her Senpai
After enough years in the presence of her "senpai", an Aishi woman will eventually develop the capacity to experience emotions, even when apart from her senpai. After several decades in possession of a senpai, an Aishi woman would no longer require her senpai's presence in order to experience stimuli the same way that normal humans do.
If an Aishi woman loses her senpai before she has developed the capacity to experience emotions, she would feel as though she has permanently lost the capacity to hear music, see color and feel warmth. This may lead her to fall into an extremely deep depression that leaves her in a coma-like state. However, if an Aishi woman loses her senpai after she is no longer dependent on his presence, she would not fall into the coma, but she would still feel an extremely deep sense of loss and pain that is far beyond what a normal human would feel at the loss of a loved one.
A senpai can influence his Aishi's personal growth and development. If her senpai says "Stop killing people or I'll hate you forever!" enough times, he could "train" his Aishi to stop being a killer. If her senpai is meek and submissive, then he would have no influence over his Aishi's development.
Depending on how the Aishi woman "developed" after acquiring her senpai, she would react to his death differently. She might enter a coma-like state, might fly into a blind rage and kill everyone around her, or might try to live a normal, happy life without him. This is heavily dependent on what type of senpai she acquired, and how her senpai influenced her personal growth and development.
It's also dependent on how he died. If the senpai died of illness, the Aishi would feel as though nobody is to blame. If the senpai was murdered by someone, the Aishi would seek revenge.
If Senpai is customized to be a girl, the Aishis will still find a way to continue their family line. It has not been explained how yet.
YandereDev imagines that Yandere-chan's great-great-great-great-great-great grandmother wore a bloody kimono and wielded a knife.
The last name "Aishi" is a play on words. Ai means "love" and Shi means "death".
Yandere-chan's great-grandma and great-grandpa were the first to move to Buraza Town. Yandere-chan's grandma asked for a basement, which great-grandma agreed to. The grandmother eventually kidnapped the grandfather and kept him in their basement. They then gave birth to Ryoba, who eventually used the basement at least once.
There is a brotherly kinship among the various "Senpai's" because they share each other's experiences with a yandere wife. Still, they are all their own unique individual.
Yandere-chan's family members are all named after blades. Her child would also have a name that sounds like a blade.