Eulalia Crivelli

Personality: Optimistic, free-spirited, self-confident, curious, good problem solver, good at connecting with others, emotionally resilient but currently grieving their dead husband heavily, unevenly mature/immature, sometimes tends to run from problems

Eulalia Crivelli is an alchemist, one of the extremely intelligent and extremely lucky few who were able to achieve immortality. They were introduced to the field at age sixteen when they married the moody eighteen-year-old Benedetto, who had become obsessed with the prospect of escaping the material limitations of mortality. Eulalia and Benedetto's partnership was awkward at first, but over time, the two bonded over a shared sense of intellectual curiosity and desire to explore everything the world had to offer. 

After nearly two decades of collaboration, Eulalia and Benedetto achieved their goal and created the Elixir of Life. They decided to fake their deaths, in order to escape the lives expected of them, and free themselves to travel the world in search of new knowledge. The two of them had gotten their wish, and were able to travel the world and live a hundred different lives in a variety of regions. The two of them rarely settled down for longer than a decade or so (and usually far less), experiencing many different connections with other people but never anything as deep as the seemingly death-defying bond between Eulalia and Benedetto.
This ended in the mid-21st century. The world had been in decline for decades, with exponentially dwindling resources (water, food, livable land) inciting exponentially growing wars and instability. In the end, even the scarcest scraps of safe living were decimated by atomic destruction.
Eulalia and Benedetto had each possessed a single Red Stone, and had assumed they were indestructible; spears, swords, even bullets did nothing to them. Neither could have anticipated the outcome when Benedetto was caught in the immediate proximity of a nuclear blast. While the elixir of life already in his system kept him from being immediately incinerated, the destruction of his philosopher's stone and the rapid dispersing of its life-extending effects meant that the radiation sickness kicked in quickly. He was barely alive by the time Eulalia was able to find him, and the agonizing ordeal of watching him die in their arms is a memory burned in Eulalia's mind for the rest of time. 

Ever since then, Eulalia has been trying and mostly failing to adapt to the fledgling society that has sprung up in the ashes of prior civilization. Their most recent attempt to enter the largest city they've come across yet ended quite poorly, and they've been imprisoned. Fortunately, they've begun to foster a friendship with their cellmate, a falsely-imprisoned bureaucrat named Guy Pérez.

Eulalia was born into the role of a wealthy merchant family's only daughter. Being an only child, their parents were highly motivated to find them a husband, even though Eulalia did not end up developing like an average woman; if they had been born in modern times they would have been recognized as intersex, having klinefelter & androgen insensitivity syndrome. Their husband Benedetto was never extremely motivated to have children (if he had been born in modern times he would have identified as gay), so he found it almost lucky that his wife was unable to get pregnant.
Eulalia began specifically identifying as nonbinary and they/them in the 20th century, but had already been conceiving of themself as something neither/both and using a combination of he/she pronouns for centuries, having witnessed many other non-binary expressions of gender during their travels.