Ancient Xi
#1 - He killed everyone from the Tang family who knew about the encounter they had earlier that put him on bad terms with the family. There isn't anyone left to hold that against him (except Tang Ruyan whom he is holding captive.) #2 - No one was around to witness him killing everyone so no one will know who did it and there isn't anyone to hold that against him. (except for Tang Ruyan whom he is holding captive) ...He is keeping Tang Ruyan captive to learn about the family because he has become their enemy..... HOW has he become their enemy when no one alive knows of anything he did to offend or hurt their family? (with the exception of Tang Ruyan whom he is keeping captive) Keeping Tang Ruyan alive doesn't make any sense to the storyline and is really just a liability to him at this point. If she manages to escape then the family would know about him and everything he had done and he would be an enemy.
All these chinese authors make their MCs so bloodthirsty at all the wrong people and for all wrong reasons. He didn't even care about that fruit to remember but now he made this family into his enemy. Later author will come up with some bullshit that this entire family is evil and MC has no choice but to destroy them. Chapters like these make me drop these novels mid way.