Li Fusheng had read quite a few Daoist classics out of sheer interest, and he strongly resonated with the Daoist philosophy of non-action and following the natural flow of things.
Therefore, after arriving in the Shinobi World and meeting Saya and Sara, he felt this was also a matter of karmic affinity.
Since he had no aversion to marriage, and Sara could help him cultivate better while also possessing striking good looks, why not embrace it?
Chapter 36