This is Aria of the Withered Branch.
Alcheris Voygianna has had enough. Enraged, purposeless, and no longer wanting to go on after years of torment, she runs away with her stepmother's ring. But when she crushes the ring and falls asleep after failing to end her own life, she dreams of five demigods, who greet her in person a week later after she awakes! Their one request to her is this: live on so that they may live forever. In return, they promise to make her life worth living, but can they uphold that promise?
When Alcheris' mother died, her father brought his mistress and illegitimate daughter home to live with them, and forced Alcheris to live as a boy to ensure that his other daughter would succeed him as head of the household, as the family tradition dictated that the next head must be female.
The father continued to favour his other daughter in subsequent years, largely ignoring Alcheris until she reached adulthood, at which point he gave her a recommendation letter for a civil service job in an embassy, and made it clear that she was no longer welcome in the family home.
Shortly before Alcheris left, her stepmother snatched the necklace she'd inherited from her mother and tossed it into the fireplace. Alcheris subsequently retrieved her charred necklace and stole her stepmother's ring on her way out of the house, then booked a room in an inn.
Upon entering her room, Alcheris vented her anger at the cruel treatment she'd received from her father and stepmother by hurling her stepmother's ring to the floor and stamping on it, breaking the jewel inside it. Tired of living, she drank a vial of poison, and laid down on the bed to die.
Rather than dying though, she had a dream about five people she'd never seen before; a little girl, a young woman, two young men, and an older man. When she awoke, she was informed that a week had passed, and that she had visitors, those being the five people she'd dreamed about.
They explained that they were 'Binah,' god-like beings with one setback; their immortal lifespans are bound to a 'token.' When Alcheris broke her stepmother's ring, she became their token, and as such, they need her to live forever in order to do so themselves, otherwise they'll only live to the age of 300.
As their lives depend on hers, these beings become a support system for Alcheris, and with their encouragement, she regains the will to live and takes the job her father arranged for her at the embassy. Soon after, she's asked to help investigate a haunted house tourist attraction where two women went missing.
Regarding Alcheris' hair length and gender identity, as a child, her light brown hair was cut short and her family made her drink a potion to prevent the bodily changes associated with puberty. As an adult, she has long hair, tied in a braided ponytail, but continues to present as male while secretly regarding herself as female.
You can read the full manhwa at Tapas.