Early Life and Geneology

Yamata Benzaiten (named for the goddess, Ben for short) was born to Yamata Orosuke and Yamata Mizuchi nineteen years prior to the events described in the manga. She and her parents were members of an old clan of demon slayers: the Yamata. The Yamata were renowned for their use of the Breath of Snake (and it's derivative: Breath of Dragon) style swordsmanship. They were also skilled goldsmiths and many of their clansmen wore trinkets and jewelry made of gold, even in the heat of battle.

Her grandfather, Yamata Hebimaru, was the head of their clan and a retired Kinoto. His elder son -and Ben uncle- was Yamata Mamushi, the snake hashira. Ben's own father held the rank of Hinoe and her mother of Tsuchinoe. They all used Breath of Snake style swordsmanship.

From a young age, Ben knew that her destiny was to join the Demon Slayer Corps. It was what her family had done for generations out of memory and she had no intention of stopping the tradition. It was an honor to fight for those who could not fight for themselves, an honor to serve her countrymen even in the shadows. She had no illusions about the danger of her mandated career path, however. Her mother was missing an eye, her grandfather, one of his legs and her father was covered in scars. It was a path that would cause her pain but one she needed walk out of necessity.   

She first picked up a sword at the age of eight, the typical age that members of her clan began training. While the other Yamata children she was in training with all set to learning snake-style swordsmanship, she was not fast enough or strong enough to keep up with them and she soon fell behind even in the basic forms. It seemed that she'd be the first Yamata in generations to be a complete failure, but her older cousin -and the snake hashira's son- Ryusuke took pity on her. Usually, the top two trainees from each class were selected by the clan head to apprentice under clan members who knew how to use the breath of dragon swordsmanship, but Ryusuke pleaded his case before their grandfather for Benzai to be one of the ones chosen.

Hebimaru refused. How could a child who couldn't even complete basic training when all other students had passed be saddled with the weight of their clan's legacy? It was decided that if Ben showed no promise as a demon slayer, she'd been married off to a member of one of the other demon slaying clans as soon as she came of age. Her parents and uncle argued against it, but her grandfather would not hear them. His mind had been made up. There was no room for the weak within the ranks of the corp or the halls of the Yamata clan. Ben would make herself useful one way or another.

In fear of her future as a former member of her clan, consigned to silence because of her own uselessness, Ben begged her cousin to help her. Ryusuke took pity on her and she began her training. During the day, she'd run through snake-style drills with the other members of her class and at night, her cousin would train her. The schedule was grueling and as a tutor, Ryusuke was relentless. Most nights she didn't sleep until dawn was breaking. 

For six years she lived this way: training with every ounce of strength she had, sleeping only when her legs gave out under her and drilling until she found herself maintaining her breathing even in her sleep. When the day of Final Selection arrived, she was shuttled off to Fujikasane mountain with the rest of the Yamata children ready for their final test. The year she went, none of her clansmen died, she saw to that herself. While on the mountain, she acted as a commander, encouraging the group to stay together and helping the weaker members take down demons too strong for them alone to handle. 

The Red Night

It was after Benzaiten had slain her tenth demon independently and risen to the rank of Mizunoe that the family decided to celebrate her success. Her achievements had coincided with the new year and the Yamata were never ones to turn down the opportunity for a good feast. They drank and sang late into the night. The clan had never been lax, even in times of celebration, but they'd been drunk off their own joy and so let their vigilance slip. Once they fell asleep,

(still writing this so that it sounds good. basically, they all got drunk as hell, a demon w a bone to pick w ben showed up with some of his homies- one of whom was a lower moon- burnt down their wisteria trees and stomped tf out of her clan. her parents and grandfather die and ryosuke gets half his body chomped on before managing to kill the lower moon.)

The Eight Heads

The morning after the attack, only eight clan members remained: Benzaiten herself, three demon slayers who'd passed final examination at the same time as her,

(also still writing this. the seven clan members who survive get together w benzai and they're like 'what the hell we gon do now' and she's like 'uhhh, let's get revenge'. they track down the stragglers, take them out and name her the new head of the clan at sixteen.)