The premise of this story is a survival story in pokemon based loosely around Castaway.
The main character is going to be visiting Alola with his family for a family vacation that they do every couple years. It is a tradition in their family to gain their starter there when they come of age to have a pokemon (age 10).
The beginning arc-
When they are flying to Alola they get stuck in a storm and the plane receives a lot of turbulence. The pilots notice that the storm is created by Thundurus, who is known to not be friendly to anyone in its airspace. Thundurus shoots down the airplane with a large thunderbolt into the engines, making the plane go into a nosedive and start to rip apart.
The main characters sibling gives them a pokeball with a Spinda, their own starter found in Ten Carat Hill, to save the main character by using Protect. They use an Alakazam to try and slow down the debris, hopefully letting others escape via a Flying type or some other means. The main character holding onto the Spinda gets ejected from the plane from an opening. While they are falling they see the plane explode, making it so no one else could have survived. Spinda uses protect right before they get to the ocean saving them from dying, but now must get the main character to safety as their last directive from the sibling.
After multiple nights in the ocean, using Safeguard to keep the young main character from contracting pneumonia or other illnesses, they are saved by a Relicanth that takes them via Surf to an island uninhabited by humans. Once they get to safety on the island though the main character is on the brink of death because of starvation and the shock of losing his loved ones, so Spinda must save them with a well timed Thunder Punch to jumpstart their heart.
After waking up the main character finds that all they have is Spinda, an eight badge pokemon with almost every known species move for him via level up, TMs, and move tutors. Their sibling put all of their effort into cultivating their starter Spinda to be able to deal with every situation, making him the clinch hitter for their team but also letting all of their other pokemon only be at about a four badge level.
The main character asks the Relicanth that saved them to go back to the wreckage and salvage anything possible.
This is the start of the survival arc-
After doing an inventory the only things that the main character has is Spinda, Spinda's pokeball, the clothes on their back, and a pokedex from their sibling that has no signal (it can be charged via the sun, and it is fully upgraded with the national dex for all regions (it also has an emergency beacon, but that was broken when they landed in the ocean)).
The first couple of days they have no food, but they create a structure to live in near the beach because every couple of days the Relicanth comes to deliver random items from the wreckage. While searching for food they find a pokemon egg that they find is parentless and keep, which later turns out to be a Spinarak egg. They use Spinarak as a helpful crafter with its webs and they start to train it once it becomes old enough (a week old).
Weeks later their base is significantly better with the addition of Spinarak in the crafting process and the random items that the Relicanth will bring regularly. On a new moon night a shadowy figure is seen outside of their camp making childlike noises, which severely bother the group. They find it later to be a Phantump that likes to play pranks, although they originally thought it could be another survivor. The Phantump joins them after a while because it is lonely being the only Phantump on the island and it is a lot more exciting with the group. Phantump is trained to help grow plants, specifically berry trees for everyone, and regularly trained for battle.
With a larger group and around 3 months of surviving near the beach with an ever expanding base, the group decides to find better materials in a cave further down the beach. They find a lonely Alolan Diglett in the caverns while searching for precious metals to help them survive. After saving it from a cave in the main character takes it back to the base, where it joins the group and helps with its development. They use the Diglett to help create trenches for seeds and because it is a part Steel type they use it to help mine the cavern they found it from. It is further trained with the group.
6 months into their solitude on the island, they haven't actually found any other pokemon except for migratory Flying types that can't grow big enough to ride. Relicanth comes back with a full suitcase which has a Pokeball inside. The pokeball houses a Pancham, that was stuck in stasis so it wouldn't stare and die from the extended time in the pokeball. He was the newest pokemon on its old team and hadn't even had the chance to participate in a pokemon battle when its trainer passed. Finds purpose in protecting the young main character, but it is an unhealthy obsession and later won't allow anyone, pokemon or human, to come near the main character. It is even more protective than Spinda because Spinda understands that the main character needs interaction.
Almost a year later Relicanth has brought everything it can salvage from the wreckage, but has found a string of nearby islands that it previously didn't know about. It decides to become part of the group after being with them for so long, even though it is one of the longest living pokemon in existence. The main character has a stockpile of resources and has used their deceased siblings pokedex to take ownership of a number of pokeballs, letting them catch all of the pokemon to be part of their team. Using Relicanth, they Surf towards these newfound islands hoping for salvation.
Return to civilization arc -
Relicanth takes the main character on its back to the nearest island, a three day journey. They arrive on the coast near Konikoni City on Akala Island. After letting their full team see the lights in the distance Spinda and the main character become emotional because they are finally able to see what happened to their family. They only problem is that they meet a lot of resistance because the main character doesn't have any ID, a reportedly lost pokedex, 11 years old (which is barely a new trainer) and pokemon that at this point are almost all fully evolved. Alongside all of this is the fact that Panchum, now a Pangoro, is so overprotective of anyone getting close to the main character, they worry that someone did something to them in the past (abuse, etc.).
At this point all of his pokemon outside of Spinda and Relicanth are almost at the equivalent of a six badge pokemon (Spinda is champion level while Relicanth is a pseudo-elite four level pokemon just do to age and not having a natural predator). Because of the fact that no one can get near the main character, they have to talk from a large distance and on top of this the pokemon choose to not be treated by a pokemon center only a Chansey (even then it must have at least one of them as a bodyguard for the main character). The police intervene at this point with ace trainers and have to hypnotize the pokemon to sleep (they can't make Ariados sleep because of Insomnia so they have to knock it out).
The main character is angry that they did this, but also understanding because every pokemon other than Relicanth have pychological problems (Ariados = has always had the main character as a parent, Trevenant = has been alone for years as a ghost type and latched onto the main character and their group, Alolan Dugtrio = same as Trevenant but it is due to its steel type, Pangoro = believes that it is the last line of defense to save the main character in case something happens like its former master, Spinda = has practically raised the main character and its former trainer's dying wish was to keep them safe). After talking to the police they realize that the main character is a survivor of the crash.
No one other than the main character survived the crash. Their parents and sibling are all dead for certain, and now the authorities know that it was the legendary pokemon Thundurus that caused all of this. After receiving the statement of what happened the police station is attacked by the main character's pokemon in a frenzy with Spinda going crazy searching for the main character and has used a Safeguard to keep the team from falling asleep, or getting stopped via status effects. When the main character is found the pokemon fall into another frenzy ready to kill the investigators, but the main character stops them and tells them we must leave to find our new home.
The search for a new home (the creation of a ranch for him and his pokemon in the region they settle down in)(at this point everyone is at the champion level) (is used as wet stone for future champions to test their worth against)(also used to give lectures via videophone to survival classes)-> the lowering of the defences (slowly getting the pokemon to let people come into contact with the main character because he is getting old and wants to settle down not just with his pokemon, but to create a new generation)(has a massive ranch all protected by his pokemon, with many rare ones within)-> the meeting of the one to open up their heart (a special person comes to visit this legendary master)(they have the ability to talk to pokemon like N or Yellow, which is the only way to get near the main character now (through his pokemon)) -> the start of a legacy (the passing on the spawn of his team to his children)-> a new generation with a new purpose, not just to survive