He started moving slowly at first since this was her first time, but also because her body resistance was much more powerful than he expected it to be.
Even though he had destroyed the last obstacle, her body was still much more powerful than his, and she had one of the tightest entrances that he had ever tried in both life.
For that reason, he had to use not only his body's strength but also his cultivation in order to be able to move his hips so that his ragging dragon could enter inside and get outside of her secret cave.
While he kept plowing her secret garden he could feel her purity Yin enter his body, pass through his meridians and reach his Nascent Soul and boost his cultivation.
At the same time since he had to use his cultivation in order to keep going, he was also training his newly gained power and cultivation.