Dimension Arc:

Leo and Co finally make it to where the Totem pokemon have made their "Base Camp" around a rozen Guzzlord, which is still frozen thanks to a nine-hundred-year-old Alolan Ninetails. The ice will not hold it for much longer, however, giving Leo a week at most to try and find a beast ball in order to catch it. One of the Totems, a Dragonite, promises to fly Leo to Mount Coronet if he does this. Leo initially wonders why they can't just hurl it into the portal as a block of ice, but the Nihilego assures him they have tried it, and the portal almost always collapses before they can get it through.

Now running out of time and knowing his team cannot help the Totems in battle, he frantically searches the islands for beast balls, the balls uniquely designed to capture ultra beasts, using his knowledge of Aether sites to help find them. He eventually finds three in a small site, and the battle begins.

The battle against Guzzlord immediately goes sideways as the combat attracts ultra beasts from all around, most of whom the Intelligent Nihilego does not control. It's a grand melee, ending in Leo capturing Guzzlord, a Buzzwole, and a Xurcitree and hurling them through a portal Kartana made, then fleeing the scene with the help of the ancient Ninetails.

Unfortunately for him, in the battle the Totem Dragonite's wing is injured and he spends the next four (could be longer, I might've made it six) months waiting for the dragon to recuperate, doing his best to speed along the process by finding medical supplies that are still good. Even with the Totem Blissey's help, however, it doesn't go quickly. He travels and trains during this time, his team and his own aura powers growing exponentially while training against ultra beasts, eventually finding all four of the Tapu Pokemon's feathers, and Dragonite carrying him all the way to Mount Coronet.

There was a possibility for a pitstop at Pallet Town, where Leo would have found a new pokedex, fixed the Porygon? Or Rotom. Now living in it, and potentially caught The Pikachu. Ash's Pikachu, who never had an Ash in this world.

There is a small town at the base of Mt. Coronet with maybe two hundred human survivors, living quietly and in relative fear of the nearby pokemon. Without the means to recreate pokeballs, they are reliant on the few trainers in their ranks to protect them – much like Pokemon Legends. They tell Leo their story when he arrives, and take him to the top of the mountain. More relics of legendary pokemon lay scattered about the place, on broken stones and pedestals, with a statue of Palkia and Dialga standing above them. Leo discovers that people have been bringing these relics back to the mountain one by one, and when all the relics (like the tapu feathers) are brought back the legendary pokemon will return to the world.

He also finds Cyrus, the cause of all this, frozen in time with the red chain wrapped around both hands. His plan only half-succeeded in this timeline, as he was eventually thwarted by the champions of this world, but the damage was done. The People still lost their Spirit – what he saw as the root cause of all problems in the world was one of the things holding it together. Leo places the feathers at the feet of Dialga and Palkia, and a portal opens for him to leave through.

Pausing just before heading home, he stops to ask Cyrus if it was worth it, almost rhetorically. Neither he nor Santiago expect to get a flash of emotion from the statue of a man, Santiago psychically and Leo through his aura empathy. It is regret, though neither are certain whether its regret for his actions or regret for not succeeding. Leo remarks that Cyrus might be the most dangerous criminal the pokemon world has ever known, and steps through the portal.

He does not go home immediately. Instead he warps to a dark planet, where Ash alongside Solgaleo, Cynthia, Victoria, and Kukui are battling against Necrozma, fused with Lunala. He enters the fray, and although he doesn't really manage to help much against the terror that is Necrozma, he does figure out that the legendary's aura is broken when he tries to use a Z-move. Instead of the move working, the aura flows up and starts to heal the cracks in Necrozma's aura – he only notices this because of the similarities between it and Spiritomb. They all use their Z-moves and pump their aura forward, eventually managing to fix Necrozma enough that it spits out Lunala. Together, Lunala and Solgaleo join the effort to heal Necrozma, sucking power from the portal Leo came through and pumping a ludicrous amount of aura into it.

The legendary is healed by this, and becomes Ultra Necrozma. It thanks them, mentioning that it was injured during a battle with an alien entity and its aura destroyed by the actions of man, then disappears entirely to go assess the damage to its multiversal "sector" while it was gone. Lunala and Solgaleo take everyone back to their original dimensions, Leo reuniting with Sunny the Meinfoo.

LORE DUMP: The alien entity that Ultra Necrozma fought is Eternatus. My theory is that Eternatus is the only truly evil and malevolent being in the pokemon universe, as it is, to my knowledge, the only pokemon to have two legendaries specifically made to counter it (Zacian and Zamazenta.) Its aura is also somewhat corrupting, as it causes Dynamax and leeches into the land.

NEXT ARC: The Alolan League

Leo discovers the time dilation of the place (maybe, maybe not, was still undecided about this) though it wasn't like he was gone for an hour or something. He was still missing for a good few months, though to be honest it makes more logical sense for it to be equal time passing. Either way, Victoria fills him in on what happened while he was gone. Ash and Gary started their journey in Alola with Professor Oak's blessing, and had to deal with a rampaging Necrozma trying to absorb both Lunala and Solgaleo. Victoria was initially shocked at how the situation worsened by their presence, but was talked out of evacuating them from the region by the Tapus, who told her just what, exactly, Ash is to their world. She didn't take this lying down, however, and formed the Ultra Guardians alongside Lusamine and Cynthia, in order to track ultra beasts and stop them before they became a problem.

Stein, the Type: Null, officially joins Victoria's team, leaving Leo.

Lusamine gave Cynthia the Magearna shell, so she now has another pseudo-legendary on her team.

This also accelerated the formation of the Alolan League, which is well on its way to being accepted by the regions at large.

Leo recuperates and theorizes that his presence may have caused some changes in the timeline of the world, as Kanto is still a hot mess and doesn't seem ready to see Mewtwo's arrival, while the Alola arcs happened early. In addition, the situation in Sinnoh is heating up, Team Galactic making its presence known and starting to aggressively hunt legendary pokemon.

This is pretty much the case, though it's not all Leo's fault. Jack's introduction of youtube and the sharing of information has led to the acceleration of many plotlines that require such information – such as Sinnoh and Kalos – and Leo was around Ash and Gary to influence them. They were not direct causes to these changes, but rather used as…pivots for the people around them to make them. If that makes sense?

During the recovery period Alola's league is officially recognized, with Victoria as its Champion. Her initial fate was to be killed during the coming conflict between Team Rocket and Lance's Indigo League, but Leo's presence caused her to make different choices and avoid that. Thereby avoiding the future Celebi showed Leo all that time ago. Back in chapter 20, I think?

Leo agrees to go to Sinnoh with Cynthia to stop what's happening over there, but not before stopping by Johto's Burnt Tower. He places Spiritomb's keystone in the tower, and is about to leave when the three legendary dogs and Ho-oh show up. The Keystone evolves into Marshadow, which bows and thanks Leo before running off after Ho-oh.

As a side-note, Ash doesn't go to Sinnoh with Leo. He either stays in Alola, or goes off to Hoenn or something.

NEXT and FINAL ARC: Sinnoh

Leo finally meets Jack in Sinnoh. They meet to comedic effect. Probably Leo punching Jack and calling him a fraud, and Jack making fun of his dancing on TV. Jack has teamed up with Colress while Leo with Cynthia to take down Team Galactic, though Cynthia has the objective to also do her gym challenge at the same time. Sinnoh needs a new champion, as the current one, while a strong trainer, is not a good leader. (FOIL to Martin, the Champion before Lance. He was a good leader, but not a strong trainer.)

Jack and Colress, both men of science, track Galactic's movements and plot out charts of their predicted strikes and operations; with the help of Leo and Jack's limited meta-knowledge. Meanwhile Cynthia and Leo act as strikers, running around battling Galactic, who are starting to come out as a criminal faction, leading to the company, Galactic Team, to try and splinter itself off.

Leo finally catches his flying-type too. Just prior to the climactic battle he heads back to Mount Silver, following his aura instincts and knowing they needed more firepower to defeat Cyrus, as he looks set to summon Dialga and Palkia. Despite their efforts. There, in Johto, he catches an Articuno.

That's why I didn't give Leo a flying type. He was gonna catch Articuno the whole time.

The whole arc culminates with the final battle atop Mount Coronet. Xena probably evolves in there somewhere, in properly dramatic fashion. Leo might have also caught a few new pokemon, like a Drapion or something. Of course the heroes succeed and the fate of the world is saved. Giratina's appearance would be properly terrifying. Somehow I'd have to foreshadow that…

Arceus might appear? Explain some of the things Leo was doing – like how his presence wasn't supposed to be there, and that he absolutely wasn't a Chosen One, but because of his actions Arceus and the other legendaries were able to manipulate events to make some things less…intensive on the world. No space-time tears that they have to fix, Ultra Necrozma is healed early and can now help stabilize events, etcetera. Like I said, Leo was a pivot. He wasn't destined to do anything, but by his own actions made it seem like it was his destiny and kinda…strong-armed his way into the world's events.

EPILOGUE:

The finale would be Cynthia versus Leo in the Sinnoh conference. Leo would of course lose, but Garchomp versus Diana; Magearna versus Articuno; and Link versus Lucario were matchups I was particularly looking forward to. That was the planned end to the series, though.