My oneshot book wasn't responding so I'll have to post the story in this book... all credit is at the end of the chapter...
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Gaster had thought of getting an apprentice for a while since he was basically allowed too at this point and was good at his craft and the way he shows newcomers basic magic and once he heard a new witch needed to be trained he took the opportunity to take them on as his apprentice...

During training he noticed how stiff and cautious his apprentice gets especially with certain magic... for instance fire they would flinch as for ice it was shivering though the apprentice had more trouble with fire then anything. After his reorganizing of his spellbooks he heads outside and noticed his apprentice still trying to get fire perfected before their next year starts so they wouldn't be too far behind. Soon he was close enough to hear a sigh in defeat and walks over "(y/n) are you alright?" He asked soon after his apprentice looks at him "oh. Hi Gaster... yeah... I'm fine..." was their reply and honestly he was wasn't convinced as he walks closer and holds their hands out so they could summon their (fav/color) fireball. "Just focus (y/n)... I'll help you..." he stated as he watched his apprentice nod and try again after a deep breath and try to summon the (fav/color) fireball again as he kept close watch he soon noticed that (y/n) was about to flinch again due to the heat of the fire causing him to rest his chin on his apprentice's shoulder. "Relax... your magic won't hurt you... your all right..." was all he said as his apprentice looked at the (fav/color) fireball as it slowly turned into a dragon causing his apprentice to smile as the fire dragon flew up into the air and bursted into some fireworks. Soon as the fireworks ended he took his hands off his apprentice's wrists and hugged them around the waist "I knew you can do it. I'm so proud of you" was all he said as he saw his apprentice blush slightly and look away a little bit and soon after he nuzzles his apprentice causing them to blush and it made him purr happily "thanks G" is all    (y/n) said as he continues to smile "your welcome (y/n)..." was his reply as he looks at the sky "should we get some sleep?" (Y/n) asks as they see the moon peaking from behind the tips of the trees "yes that I think is a good idea" was his reply as he walks over to their shared living quarters since his home is small and he let his apprentice have the top bunk though he didn't go to bed like his apprentice did but wrote a letter that basically was like an update on his apprentice's  studies and he wrote '(y/n) is starting to get the better at handling fire magic now and it makes me proud to see how far they came. From not being able to do a single spell or magic off off was expected for a beginner but during the years I've been teaching them they started learning more and more and I will continue to teach my apprentice and not give up on them. I'll give more updates next month.' Is all he writes and then signs it then sends it by owl to have it mailed then gets ready to sleep but there is one thing he now knows all to clearly he loves (y/n) and not just because they are his apprentice it's because he got to know them, teach them, and be close to them. Gaster was not that good at relationships and didn't know how to say anything but since his apprentice was asleep he decided to use it to his advantage. "Goodnight (y/n)... I love you..." is all he said as we got into bed but what he didn't expect was a reply "goodnight G and love you too..." (y/n) yawned out and fell asleep and caused Gaster to blush a dark purple but he wasn't just embarrassed. He was also happy as he fell asleep along with his apprentice to the dream world.
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Author's note.

Alright so yeah... my oneshot book is not responding so I'll post this story here...

And two this is a story I decided to add to... the real concept of the story belongs to EmilySkelewolf

And so does this chapter of her gaster oneshot book which is book 4 in the series she has...

I own WitchTale!Gaster

Emily owns the story...

Though I hope you enjoyed this and perhaps I could do an rp with this AU... I wouldn't mind at all...

Emily I really enjoyed this chapter in your book and not because it had a Gaster I made...

Though in hindsight Dusk [Umbreon!Gaster] is the most mature out of all of my gasters...

And I apologize for this story being long as well...

Anyways see you in the next chapter my fluffy clan members.