>>280075750I've looked at his abilities, how exactly does he defeat Saitama? I'm not even going to use any narrative advantage or say that Saitama is invincible or gag to justify Saitama resisting his ability. Let's just use feats to satisfy you.
Regulus would lose to Ram, who is much weaker than Saitama and is all raw power.
Regulus van ignore durability? Ok, but his attacks have speed, even assuming Saitama stood still and let him hit him his reaction speed and speed in general are enough to notice being cut and dodge the rest of the attack before being cut completely.
If Regulus is pushed too far from his wives their connection is severed, so even assuming Saitama didn't want to hurt anyone around him and didn't kill his wives by accident he could sever Regulus' connection with his wives by pushing him far enough, which would happen when he hit him.