EXPLANATION: Mizuki never really completed GENO... but on her first run, she went GENO until she met Papyrus yes... that means she killed Toriel on her first run... remember, her goal was to avenge her parents, but when she met Toriel, that's really hesitated to continue GENO unfortunately, she did kill her anyway, but not the donk way... she fought for real, but she immediately regretted it... although, after meeting Sans and Papyrus she started to regret even more she still continued to kill every monster, but on the last fight with Papyrus, when he spares you, she couldn't take all of this regret anymore, she couldn't fight him, he was too sweet and pure... she couldn't so, after she spares Papyrus, she decides to reset and re-do it all over, the right way, the Pacifist way! she still regrets it tho... and she knows Sans knows her sins but he still has nightmares of IF she actually DIDN'T spare him... he's not actually having nightmares of her past resets! those two times were the only times she reset! Mizuki promised not to reset or go GENO ever again... Sans takes time into trusting her... and even after he did (which, in this comic he does) it takes him some time to stop having those nightmares...
go here if you cant see clearly:Â http://yumitsukiyoru.deviantart.com/art/You-Worry-too-Much-Entertale-635120659














