"Negative Hero and the General of the Demon King's Army"

Notes:

An on-going wholesome web-manga series by a pixiv artist named "Hama Chon"
The story as I understand it:
A lonesome, broken Hero named "Renée" confronts the General of the Demon King's Army "Gouma Hyudor." However, as the battle starts, our hero finally gives in to despair after bearing the burden and responsibility of the title of "Hero" forced upon her by her people. Hyudor, harrowed by Renée's dreadful emotional and mental condition, quickly takes her in his fortress to live a new life as his new assistant.

Pixiv Source List.
As always, translations are available in Safe/Danbooru.
However, it's still fairly new and slowly updated. Like 23 pages since the 6 months the artist uploaded the first chapter. Still, it's quite a good read. Very cute and endearing. Plus, Hyudor is a really cool guy.