One of Yousuke's love interests from the other world will find a way to follow him to Earth by the end of the series.
Because lets face it, he deserves a happy ending and the author wouldn't go out of their way to make him so endearing only to give him a sad ending.- I wouldn't be surprised if all three girls found a way to reach Uncle.
Before Uncle returns home, he sets Elf-san on a throne.
- As she has been revealed royalty in exile, he may help her get a seat on the throne.
Uncle’s relationship with his harem will be revealed have indirectly helped him get home.
- It will probably come about by a combination of Elf-san’s ancient artifacts, Mabel’s sword, Alicia’s missing memories and his own attempts at creating a foe so powerful that when he kills it, it will cause a warp in space-time that will take him back to Japan.
The lyrics in "Story" could be the last words Uncle heard from his friends before returning to Earth.
The opening song for the Isekai Ojisan anime has the following words at the end: Trust yourself. Don't be naïve. Save yourself. Don't forget. These words eerily sound like things his friends would say if they were engaged in a Total Party Wipe battle as Uncle returns to Earth. For example an exchange could go like this: To a second guessing Uncle, Elf-san says, "trust yourself;" a snarky Mabel tells Uncle, "don't be naïve;" a vanishing Uncle calls back, "save yourself;" and Alicia cries, "don't forget," as he finally departs.- The lyrics of the song itself can be summarized as: "Don't dwell on the hardships, regret, and mistakes you've made in life. Keep moving forward towards your dreams and you will succeed." However in another way, it can be interpreted as someone trying to convince themselves that it was okay to leave things behind with no way to get them back...
There will be a plotline about Uncle (or someone else) staying in a shapeshifted form for too long
Its been established that The Mind Is a Plaything of the Body is the reason why shapeshifting magic is considered forbidden, yet uncle has shown a willingness to use it somewhat careless for rather mundane purposes. No only that, but Takafumi; someone much less experienced with magic than his uncle, also has gained the ability to shapeshift. This all lends itself to the possibility that one day one or both of them will stay shapeshifted for too long and suffer from noticeable mental effects (so far the mental side effects have been fairly minimal), possibly requiring a third party such as Fujimiya to fix the situation. Such an event could also serve to allow uncle further insight into the minds of motivation of elf-san as well. Elf-san died helping Uncle return to Earth.
There is strong foreshadowing something tragic happened to Uncle, given Takafumi's reaction to reading his erased memory diary. Uncle got himself drunk when seeing a memory of Elf-san crying herself to sleep when Uncle unknowingly rejected her offer for sex. There is another strange comment made by Uncle, when he shaped shifted into Elf-san, where he comments regret about not understanding her feelings sooner. Uncle's recollection of Elf-san being tsundere make even more tragic sense if he erased memories of her feelings for him. Uncle also made a strange comment about seeing resurrection magic only used once in the other world, and that only gods could do it.My working theory: Elf-san suffered a fatal wound from the Eldritch Abomination that Uncle summons to create a portal home. She makes a Dying Declaration of Love that even Uncle's Oblivious to Love cannot ignore. For the first time in his life, Uncle realizes there could be things more important than SEGA. He goes on a Roaring Rampage of Revenge and defeats the Eldritch Abomination. Killing the Eldritch Abomination was God's purpose for summoning Uncle in a Self-Fulfilling Prophecy. God offers Uncle a final wish as a reward. That wish is Elf-san's resurrection. At this point, maybe Uncle wants to stay in the other world, but his time is up and he couldn't make that wish to bring back Elf-san. As he is being sent back to Earth, regret sits in. He erases his realization of the feelings Elf-san and all the other girls had for him.
Alicia gets her ring from Uncle as repayment for being the Hero.
Uncle lets Alicia get credit for all his heroic exploits because he considers the fame to be too much of a pain. At some point the responsibility of being the Hero will cause Alicia some kind of hardship, and Uncle will apologize by giving her a ring to sell. Cue another moment of angry Elf-san. And Mabel. Alicia can cast water magic.
Three individuals were inside the Wand of Salvation's synchronization spell when Alicia gained Power Copying: Raiga, Edgar, and the innkeeper's daughter. The innkeeper mentioned that his wife and daughter are water sorceresses, and are why it only takes three people to operate his hot spring. Alicia has Raiga's and Edgar's battle abilities. It makes logical sense she also has the daughter's water magic. Uncle is responsible for Alicia's missing childhood memories
Given the other powers Uncle's shown off, it's entirely possible that he will eventually end up using Time Travel to visit Alicia's past and save her from the attack that kills her family. This means that Alicia is in a Stable Time Loop and her lost memories are to keep that fact hidden from the audience. Uncle is (or became) a Chaste Hero rather than a Oblivious to Love hero.
Early on Uncle made very clear he was set on finding a way back home. At some point he deliberately decided not to fall in love since that would make his decidion to leave Granbahamal much more difficult when the time came.