I have an interest in Warhammer 40K and I wanted to make a lore-accurate chapter of all female Space Marines. Here are some ideas I had.

1) A company of Space Marines become isolated in an area of space where human populations are disproportionately female with few males around. This leads to experimentation to create female space marines out of desperation.

2) Among the successful attempts is a figure known simply as "The Lioness." She becomes the basis for new Gene-Seed for all future recruits with the chapter being called "Daughters of the Lioness."

3) Thinking of making their original Primarch Vulkan with the lost company being Salamanders since I like the fact that they care about civilians and I think it would be neat to give the Daughters similar beliefs and rituals.

4) Thinking that the Daughters have male concubines as a unique type of serf. The idea they work under is that girls born of a Daughter might be more capable of surviving the process of becoming a Space Marine.

Just to clarify, my knowledge of the setting is limited as I am a casual fan. I'm happy to hear any advice to refine this or learn more about the setting. Thank you for reading!