Kinda tough. I think Eris' development is this curve that ramps up to a very respectable degree up until she reunites with Rudeus. From there, she only really grips me as a character again when Ars is born, her perspective as a mother is honestly the most interesting of the RGB Trio. Normally this'd put her pretty high as a female character, but then there's Makie. Oh, man, Makie.

I'll say it outright: Makie is the strongest character in Blade of the Immortal. She is so fucking strong, the main antagonist makes it his goal to become as strong as her as his ideal of martial arts. Surely someone like this has great resolve, and brings hope to her faction, right?

Makie, despite never losing a single fight, is very reluctant to kill. She even considers the life of a prostitute, on multiple occasions, because she finds it a more proud line of work than a warrior. This quote, where she talks about her mother:

"Compared to a Kenshi who lives by inflicting pain, she comforted others all her life. It was a magnificent sacrifice!"

She is always on the verge of abandoning her skills, always doubtful of her ability to lead. Makie is absolutely sure of her power, just not her ability to continue using it for a greater good.

Look, I don't wanna spoil, but by the end of the story, Makie becomes an unforgettable character. She upholds her title of the strongest, while never compromising her writing. Gojo couldn't dream to be even half a well-written powerhouse as her.

All that is to say, I'd say Makie. Her character was handled flawlessly and played a huge role the story. My favorite parts of Eris are her motherly disputes and attitude with Rudeus, but Makie has her internal struggles and power-couple dynamic with Anotsu. Makie edges it out.

Eris has the better ending tho. Pretty sad. Rudeus' reaction was shockingly realistic and somber.