Error waited for them to accept the vial. He wasn't this patient, but he was desperate to see HER again. Chara walked towards him. Error was getting his hopes up. "Are you sure this is not a trick?" Chara asked. Error was about to reply but Frisk said "of course it's a trick! He's gonna try erase our universe again!". Error regretted his decisions before and wanted to start a new life.
He was angered at what Frisk said. He took Chara's hand and placed the vial in her palm. "Please…" he lowered he's head for them to not see tears in his eyes; for them to not see that he has a weakness "I just wanted her back". His voice is more glitch than usual. "Set her free, take care of her, I just want to see her smile again" Error said. He teleported somewhere else, leaving behind the vial in Chara's palm.
Chara examined the vial. It seemed like it cracked. "What are we going to do now?" asked Queen Toriel. "We throw away the vial, that's for sure" Frisk said. Chara remembered at how helpless Error was and said "no" to the shock of everyone.
"Are you insane punk?!" Alphys asked. "Y-yeah. E-error i-is a disruptive or-organism. R-remember w-what e has d-done?" Undyne stuttered. "That wasn't him. He was trying to help us" Chara added. She walked towards the others with a smile and gave it to Asriel. "Take care of this Azzy" she said.
Asriel was a little bit terrified of this responsibility. He can be clumsy a dizzy sometimes. Asriel put the vial in his pocket. The whole group started to discuss this. Most of them have negative thoughts towards Error but somehow, Chara was able to convince them.
In a tree near the group's picnic, Error watched them. His tears were rolling down. "Someday, I will see her. I will see Brit" he said and opened a portal. He went in and headed to another AU, sparing Underswap one last glance before he closes the portal.