After Nobita was doing a long interogattion to Sewashi and Doraemon. He finally knew that both Sewashi and Doraemon was coming from the future to change the future of Nobi family where the Nobi family in the future was poor and almost bankrupt, because of Nobita laziness and stupidness.
Nobita was feel insulted after he heard the explanation about him that are lazy and stupid also crybaby. If he act like that and didn't act tough when he was still live in America then he will be bullied by the other student in America. Thankfully when Nobita was and his little sister was almost killed by a vampire in America. Shirou was helping them, and Shirou train Nobita to became strong, smart and a good person who love to help other people.
So Nobita are having ability to fight back when he was bullied by other people. And his grade at school also the best. He maybe not popular because of his cold attitude, but no body was to mess up with him because he is the favorite student of all the teacher in the school because of his grades.
"Sorry to made you disappointed my great-grandson from the alternate future, but sadly I was not lazy, stupid or crybaby. If I act like that in America then the bullying that I have in that country will be more severe," Nobita said with a serious expression on his faces. "So after I release both of you from the Black Keys, it will be better if the two of you are going back to your own timeline and never going back to this era. I didn't need a help from both of you got it?"
***
Nobita words of course making Doraemon and Sewashi feel shocked, but they also feel relieved at the same time. They didn't want stay at the wrong era more longer, beside that they need to find the correct timeline where Nobita was stupid and lazy. Not a timeline where Nobita was superior and smart.
"Onii-chan the boy that look like you are going here to change his future right?" Asked Tamaki. "But are they didn't know that according to the laws of physic changing the past will not changing the future, but only make a new timeline. Because if you going to the past that past will be your new future. Like the theory of Grandfather Paradox when someone trying to kill your grandfather to kill you so will not born in the future. Both of them are trying applying that theory by changing grandfather fate, but sadly what they are trying to do only will make an alternate future not changing the era where they come from."
Tamaki explanation making Doraemon and Sewashi jaws dropped they didn't expect that a five years old girl are saying a very complicated thing like that.
"Maybe the law of physic from the future where they come was different from ours or there is someone in the future that making the laws of time travel different from it supposed to be," Nobita said who feel a bit suspicious with the alternate timeline where Sewashi and Doraemon come from.
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After Doraemon and Sewashi are free from the bind of Black Keys. Doraemon was still thinking about the theory of time travel that come out from Tamaki mouth, because Tamaki explanation was made sense. But he choose not thinking about that theory too deeply, because his main priority was to going back to future with Sewashi.
"Now because I already freeing both of you from the Black Keys, please going back to your own timeline," Nobita said with a sigh while he putting back his black keys back to his pocket dimension.
There is a lot of thing that Sewashi want to know about his great grandfather from the alternate past, like how he can become a vampire hunter at a very young age. And how he can taking out something out of nowhere like that, are he have a four dimension pocket like he or Doraemon or he have something similar. But sadly because he must to going back to the future he doesn't have time to asking all of the question that lingering inside his mind.
But right when he and Dorameon was about to use the time machines so that they can going going back to the past. Suddenly Nobita was throwing a big heavy sack that full of gold to them and said;
"I knew that in your era the Nobi family was very poor and almost bankrupt so use half of the gold that I got as the payment in my job as a vampire hunter to make the Nobi family prosper once more. Even though you are my great grandson from alternate future but you still have a blood relationship with me. So it was my duty to help you."
Sewashi and Doraemon was didn't believe by what they see in the big sack. A lot of gold ingot, even though in the twenty second century making a gold was easy with the tehnology that exist at the era there is a law that forbid to make your own gold to sell. To make the price of gold keep stable.
But because the gold that they got from Nobita was a pure gold ingot from the past he and Doraemon can selling it for a high prices. Because that gold was count as a rare treasure and the prices will be more higher that the prices of the gold of that era.
"Th-this is too much great-grandfather I cannot accept it!" Sewashi said with a paled faces.
"Just accept it, I still have a lot of that gold in my pocket dimension, beside that I can still earn more gold from Shirou-Sensei if he give me another mission to kill a supranatural entity," Nobita said while forcing his great grandson to accept his gold. "With that gold you didn't need to go to the past to change the future. Because according to Shirou-Sensei making too much alternate timeline will be bad for the stability of time and space."
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Sewashi can only accept the gold and the putting the gold inside his fourth dimension pocket. His family really need that gold for a lot of things, but he knew that he cannot take the gold with him just like that without giving something back so he decided that he will give Doraemon to Nobita as a thank to giving him the gold.
"Great-grandpa I cannot accept the gold that you give to me, without giving something back to you. So I decide that I will leave Doraemon here with you so that he can help you if you need a help to solve a problem you cannot solved. He maybe an old model robot that was cheap because he lose one of his screw in the factory he was made. But I assure you that he was still more advanced the any robot that exist in this era! Beside that with a lot of cheap eh no a lot of useful gadget from the future inside his fourth dimension pocket. Your daily life would be more easy!"
Nobita really want to reject his descendant from the future offer, because he really doesn't a gadget cat from a future. By using the Structural Analysis that he learn from Shirou, he already check Doraemon body and he found out that Doraemon body was full of flaw and defect that hasn't fix yet.
But because he can see the sincerity of Sewashi he can reject Sewashi offer aside from that Nobita can see that Tamaki was have a great interest with Doraemon. And Nobita was thinking that he can use Doraemon to help him in taking care off Tamaki.
***
Doraemon want to protest to Sewashi because he was about to left behind in the past. But he cannot protest at all because Sewashi already programming him to help Nobita and his family. So he just can only accept his fate to become the helper for Nobita.
***
"Hmm this is really unexpected, I didn't think that Nobita will still got the real Doraemon even though we already changing the timeline. I think having Doraemon as his helper are his Fate that we cannot change at all no matter what," Shirou said who didn't expect that Nobita will still have Doraemon even after he and his harem change the fate of Nobi family.
"It will be interesting to see what kind of thing that he will get if Dorameon was with him, a comedy that full of unfortunate event or a serious drama that full of sadness?"
"A comedy that full of funny event was better for him, Emiya-kun," Rin said while smiling. "While we will be the one who will be eliminated any unknown factor from behind the scene until he was ready to embrace his destiny as the protagonist of this world that have destiny to save the world."