Identification of a feudal era / demon protagonist manga I'm gonna put in items what I remember


The manga is on the feudal era
The protagonist is part of a demon society, they constantly fight with the humans
The leader of this society is a giant frog, or something similar
The protagonist kidnaps a princess (or just a regular girl, don't remember)
The protagonist is respected by others, since he's one of the most powerful demons, if not the most
The protagonist respects the woman he kidnapped
In the final chapter, she die trying to protect him after the war stopped
I'm not sure but I think either the protagonist or the woman he kidnapped is named Momo, or simplified to Momo


May be really vague, but I can't remember anything more.
If I'm not mistaken, it's already finished.
Found it: Shinobi no Kuni


  Synopsis (MyAnimeLIst)
  
  Based on a novel by Wada Ryou, "Shinobi no kuni" brings a story that blends history and fiction as it shows the struggles happening during the 16th century in Iga, a region famous by the Iga Shinobi, the ninjas from Iga.


The protagonist name is actually Mumon, not Momo as I said. Would be hard to find it with a wrong name.