Zhang Yue was already sitting on Zhang Fei's lap in the lotus position, their genitals connected to each other, their eyes tightly closed, with her hands around his neck and his hands around her waist.
Unlike their usual dual cultivation, their Yin and Yang Qi did not move independently. Instead, their Yin and Yang Qi merged into one in perfect harmony, continuing to revolve within their bodies at a speed significantly faster than before Zhang Fei installed the Yin-Yang Harmony Array.
Although the amount of Yin Qi he got from his big sister was not very large because Zhang Yue's cultivation was still in the core realm and Zhang Fei's cultivation was in the earth realm, it was not a big deal for him with the Qi amplifier of the system.
Instead, Zhang Fei's Yang Qi became stronger and stronger for Zhang Yue, and her cultivation kept increasing, especially after he activated the harem sharing to share his qi with her.