(Gaster's POV)

Gaster wasn't really expecting for his son to appear in Waterfall after the day before, sure Sans would spend the day with the human girl rather than come to see him. Instead he felt his son appearing in the hall, laughing when his son knocked on the wall playfully.

"Hey Dad, I can't come in without the door. You should start just leaving it until the reset, just to make things simpler." Sans said, even as the door appeared for him. Gaster chuckled as his son walked in, very glad to see the tiredness gone from his face and a bright smile there instead.

"I did not expect to see you today, my son."

"Yeah, well Frisk and I decided to mark everything I know about the followers down and then I stop by and let you write the list of needs for what we gotta do. Well and Frisk made us lunch." Sans answered, reaching in his jacket to pull a fairly large bag from his jacket as he sat on the floor. He moved closer to his son, once again surprised at the girl he had only just met.

"She made me lunch? Why? I do not need food any longer."

"She figured that much, Dad. She just wanted to make you happy and food makes her happy. She is a pretty caring girl. The only thing she really wants is everyone to be happy. Even Chara." As Sans spoke the lost child's name his voice grew darker, as if his anger could not be hidden from his voice. The sound had Gaster clasp his son's shoulder, looking at Sans curiously as he pulled a couple bowls of soup and crackers from the bag. As if he felt the curiosity Sans sighed as he handed a bowl and spoon to him. "Apparently, after scaring her in her dreams, the fact Chara showed fear humanized him for Frisk. Now she is talking to him, well she talks out aloud while he talks in her head anyways. And he apparently is being an ass to her about something, cause she has to tell him to stop a lot. And my temper flared when he started talking, which I am sure he made fun of me for since I can't actually knock him down a few pegs while he is in her head."

As he spoke Sans opened his own bowl, lifting a spoon to stir the contents for a moment. Carefully Gaster opened his own bowl, surprised at how good the soup actually smelled after so long with no food. "It sounds a bit like you not only dislike him for scaring her but from jealousy."

His son scoffed then paused, shrugging with a sigh. "Maybe…. I don't like him being in her head in general. I also don't like knowing what he is saying. He made her upset this time. Apparently… Well I guess I already knew she had the same feelings I do but I understand why she wasn't saying anything. Anyways he was picking on her for it. I had to basically confess to her so she would realize she didn't need to worry. I knew, and I felt the same, and there is nothing that disembodied ass could do about it."

Gaster chuckled as he ate a couple spoonful of the soup, his hands slow and steady as he listened to his son rant about Chara. It was interesting to see that Sans hadn't lost some of his temper while he aged, only learning to control it better. "You always were a hot-headed child, my son. I doubt Chara would waste the opportunity to be free by push too far. And remember it should not take too long if we are successful with everything."

"Maybe but that doesn't mean I have to like him."

"This is true but remember to stay calm. You explained what you could I assume?"

"Yep this morning. Then we did the list and she made lunch. After you write your list I am gonna head to the surface. I didn't grab stuff to clean up or any clothes for either of us. Also, gotta get anything I know isn't in the true lab from Alphys. If anything is large enough I gotta also make sure they meet us in Alphys' new lab so they stay away long enough for us to finish…." After a moment's pause he looked up at his father with a curious look of his own. "I did wonder how you were going to get a full-sized soul out of a piece of one."

"That's simple. One of the things I need is a soul sample jar. Adding Determination with a human soul piece, as well as giving said piece time and talking to them often, helps it grow into its own soul. I am sure your human has already assumed as much, and has told Chara. This means that when I receive the piece it most likely be completely infused with Chara's consciousness, which means the soul that will grow will be that of Chara's, not of Frisk's."

"Wow…. And you are probably right. Frisk has spent so much time studying souls she is practically an expert in her own right."

For a few moments they sat in peace, eating the soup comfortably with one another. After a little while Gaster placed his bowl down, smiling gently at his son. He may have been gone for a few decades, but he knew his son and knew something was bothering him. "Son, if you need some advice you can tell me."

"I… Frisk and I want me to be able to remember her. She even planned to use an echo flower till she realized there was a chance her message wouldn't stay when she reset. I have no idea how to make sure I will know her when I see her. I can't stand the thought of not knowing who she is when she walks out of the ruins."

"Son, the answer is simple. You could have a picture within your pockets, as long as you are wearing something you would typically wear when a reset happens. Another solution is the hidden room you have always had on the side of the house and thought I didn't know about."

His words bought a look of momentary surprise as he mentioned the room, a look he had waited years to get for telling his son he already knew of his hidden workshop. Sans lifted a hand and rubbed the back of his head, chuckling as he looked across the room with a grin. "I should have known you knew about that room. But how will the room work, and how would I even know to look in there?"

"Simply put, leave yourself a message. In the right-hand pocket, where you never remove your hand unless your jacket is removed. All it needs to say, to not mess too much with the timelines, is that you should look in your workshop. In there you keep whatever it is that you believe will remind you. I would suggest a picture of just after leaving the underground, personally, with a note explaining things. That way you would see her face as well, allowing you to remember her face when you meet again."

"Dad that is perfect! I can't believe I didn't think about it. And by using what is an old picture in this timeline her face will be more like the face that she will have when she walks out of the ruins."

"Exactly what I meant, my son. Now hand me the notepad I will be writing in. I am sure you have a lot to do shortly."

"Yeah, you're right." Sans handed him the notebook he brought with, still eating his soup on the floor while he opened it. Seeing the note to him he spent a few moments reading it before noticing the new notes written at the bottom.

I told Sans, despite how I knew he would react. Thank you for calming him down and letting us know you already had a solution. Chara is suddenly talkative, something he hasn't been in quite a few resets. I see no problem coming from this for the most part, other than the fights between him and Sans. Hopefully Sans and Chara won't get too bad before we can move Chara out of my soul.

He chuckled at the words on the page, turning a couple pages back to write his list as Sans looked up at him. "I love a good joke."

"Ah no joke my son. Just a note she left me in here. Funny to me only because she does not realize as angry as Chara will make you, you will control your temper for her."

Sans chuckled a bit, nodding in agreement as he covered his bowl and replacing it in the bag. "Yeah, I'm just lucky she didn't find my anger scary. Probably cause it wasn't aimed at her."

Gaster made a small noise of agreement as he began writing, glad his son could at least read the script he had used since childhood. Like any other skeleton, he had his own way of speaking and writing that differed from all others in the Underground. Fortunately, skeletons could understand one another, despite the differences, making families easier to have. The thought of that had him pause, knowing that he and his sons were all that were left of skeleton monsters. Noticing the pause Sans looked up, concern showing in his eyes. He smiled to his son and shrugged, returning to his writing. "I was just thinking about how, with me technically dead, you and Papyrus are the last of the skeleton monsters. Unless the pair of you are lucky enough to have children that are skeletons as well…... Well I wish not to think too hard on that."

"You don't need to worry too much dad. Pap has been dating, against my consent mind you, Mettaton. If they are in love as everyone seems to think they are there will be a few baby bones running around. And just so you know, Mettaton is technically a ghost monster, which is a bit more likely to create a skeleton than some of the other monster types. Alphys did some research on it since the two were dating."

"And you?"

"I don't think human and monster mix dad."

"Ah I see. So, she has that much hold on your heart?"

"It's more like we have a bond of some sort. I have no clue if it is the same, or weirdly the same and not, as a normal soul bond between monsters. All I know is I can't imagine not having her around. And I had a feeling like that when I first met her in this past true reset. I had no clue who she was, like I was supposed to. I just knew that promise or not I couldn't allow anything to happen to her. I even started thinking of her as my human long before she reached the judgement room."

Gaster chuckled as he wrote, understanding that bond well. The boys' mother would be so proud of them if she still lived. The pair had grown so much, and hearing of how strong just Sans' bond was …. Well he knew if she were still alive she would be already planning a mixed-race wedding of some sort for them. "I remember that feeling well. I had it with your mother when we met before the War. I still miss her to this day."

"Don't scare me, Dad. I know mom is gone…. but if I lost Frisk…. I dunno how you kept going."

"My baby bones boys needed their father. Our people needed a compassionate scientist. I had too much riding on me to give into my grief. However, many others fell down due to the grief, too many too name. There was little we could do about it, as we monsters can not survive through grief easily. I would not wish such grief on either you or Papyrus. I would harm any that would cause it to you. And that means I would die to protect both Frisk and this Mettaton so neither of you would have to experience it."

Sans was quiet for a moment, thinking over his words as he finished his list. As he closed the notebook his son stood, facing him with a wry smile on his face. "Dad, knowing you would protect Frisk means more than you can know. It helps me understand I really misremembered you until now. And it lets me know that you will do whatever possible to make sure nothing befalls her with her trying to rescue you all. So, thanks."

"So formal. But it is no problem my son. Now here is the list of required items. The Determination young Alphys was using should still be in the true lab. As Determination without a soul to guide it does nothing at all it should still be perfectly fine to use to help Chara's soul form from the piece of Frisk's. The rest I am unsure of, as it has been two years since everyone left."

"Wait… so you only know things if people are in the Underground? How does that work?"

"What the followers hear and what I gather when the door appears on its own. Between the two things I know almost everything that happens in the Underground."

Sans paused, obviously thinking before grinning and laughing softly. "Dad you just proved your own theory about the followers. If you know what the followers hear then you are connected to them in some way. I wouldn't be surprised if they each hold a piece of your soul. That means if we are able to find all of them we just need to figure out how to get your soul from them."

"Yes, but what if what gives them life is my soul?"

"Then we are in a moral issue. You aren't fully alive without those pieces but those pieces bringing them to life means that to get them we will have to kill them…."

Gaster watched his son running through things he had had many years to figure out, his eyes going dark as he thought out the entire thing. Finally, he opened his eyes, obviously frustrated with the whole thing. "I literally can not make a decision on this. On the one hand, you are my father. I want to have you free and alive. On the other, if we take back your soul they die. I am on the fence about that and I know that Frisk would be against it if we are right."

"Yes. I went decades trying to decide whether I should make such a choice if I could. I could not come up with a good answer. Of course, this all resting on the fact that they are sustaining life via my soul. If they are not, and their bodies simply hold a piece while they have their own souls, then it would make things much simpler. The odds for that however…."

"I guess we will have to see when we find them and decide from there." Sans said, frowning. He chuckled at his son, proud his son had such integrity. "Son I am so proud of how seriously you are taking this. Please never change."

Sans grinned at him and shrugged as he headed for the door, waving back at him as he walked. "Don't worry Dad. Frisk would be too upset if I changed for me to even think it."