The Slutty Adventures of Magical Princess Makina (淫紋魔法姫マキナのビッチな冒険)
Author: Hayakawauka (ハヤカワウカ)
Label: Beginning Novels (ビギニングノベルズ)
So, yeah, it's NTR, but (in my opinion) the good kind of NTR: from the girl's POV and (mostly) consensual. This is an LN release of a WN and each chapter has a bonus alternate ending showing what would have happened if she stayed in each town instead of continuing her journey.
Table of Contents:
Novel Original Chapter: Night of the Magical Princess and the Black Knight