Because he had spent so long living out his retirement in Anti-Entropy while recovering from illness, Siegfried naturally needed ways to entertain himself, such as reading novels.
And the novel he had been following recently was precisely "The Wonderful Adventures of Honkai." The moment he heard Mo Yi's familiar pronunciation, he thought of that blond man whom he had associated with another immortal blond man.
Siegfried: Could he really be stopping time?
In fact, while that thought was forming in his mind, Mo Yi had already completed a series of actions, yet his brain had received no pain signals from his body's nerves.
Within the gray world of stopped time, Mo Yi walked up to his father-in-law and gathered a great deal of Light of the Heart in both fists before unleashing a rapid barrage of punches at Siegfried.
"Give me back my handsome face!"
As the fists infused with Light of the Heart struck Siegfried, they injured him even as they healed his wounds. The extremely concentrated Light of the Heart was even rapidly healing the old injuries within his body.
Mo Yi was not some demon, after all. How could he really beat up Siegfried, who was practically his father?
This was merely a necessary side effect of treating his injuries. His father-in-law would surely understand.
Appendix: True Kiana Arc, Episode Seventeen: After Mo Yi took the initiative to bring it up, the hesitant Mei finally made up her mind. Looking at Mo Yi, she said, "I have a friend—" Mo Yi: That opening sounds awfully familiar?! Mo Yi resisted the urge to quip, This friend wouldn't happen to be you, Miss Mei, would it? and listened on. "She likes a boy, but she doesn't know whether he likes her back. She's been troubled these past few days