The Dotharl tribe of the Azim Steppe gets covered quite extensively in the Stormblood MSQ, so if you're really wanting to get the most info, I'd definitely recommend pushing to that zone and doing all of their side quests.
In short though, the Dotharl are a people who've earned a fearsome reputation as fierce warriors because they do not fear death. They do not fear death because they believe that if they die a good death, their soul will be reincarnated within a new baby born that year. The gender of the child does not matter. A soul can be reincarnated as a woman or man - but the name of their soul remains and is given to them by the tribe's Khatun. Despite the Dotharl's reputation, they are more accepting of outside clans than some of their kin - in that they believe that those souls belonging to other tribes can die honorably and be reborn among their tribe as Dotharl.
You can find out more lore in game or in the links below! Hope this helps! ^^
- Au Ra Lore
- Dotharl Tribe Lore
- Xaela Warrior Job and the Will of Karash