An Unorthodox Guide to Conquering Another World

Generally speaking, when you start a second playthrough of a game, you'll want to take some routes you wouldn't have dared to take before, and try some options you wouldn't have dared to try before, right? Like, trying to romance characters you couldn't romance before, right?
After transmigrating to another world, Ya Feng becomes a hero. His main quest is to adopt a demon princess who has fallen on hard times and raise her to become the new queen.
Hmm, is this a female empress raising story? But thankfully, Ya Feng got the perfect strategy system. As long as he follows the strategy, he can reach the most perfect ending.
So he meticulously followed the strategy, painstakingly nurturing the princess, caring for her, protecting her, and guiding her in the right direction for her life.
He thought he could have a wonderful retirement, but he died on the expedition.
"Congratulations on achieving a perfect ending, becoming a legend of the kingdom, and living forever in people's hearts! The princess has transformed her grief and anger into strength, and will lead the people to victory!"
Ya Feng was so angry at this stupid system that he laughed.
Fortunately, he was reborn.
But this time, he's going to take the "if" route.
...
The princess stood before him again, and asked warily:
"Did you adopt me for a specific purpose?"
Ya Feng chuckled.
"Starting today! Prepare to be my slave, cook and do my laundry, and pay back everything you owed me in your past life!"
"???"