What If Ash was in Pokemon Horizons?

From So Far Away

While the Brave Olivine is falling from the sky following the Black Rayquaza crashing into it, Spinel appears at the Levincia Lighthouse aboard a helicopter. Since Rayquaza is still in fighting fit even after everything the Explorers admins have thrown at it, he tells everyone to retreat. The admins agree and leave the site. At the same time, the Brave Olivine makes a successful emergency landing in the sea nearby, with its crew calling Friede, Ash, Liko, Roy, and Ludlow to assure them that everyone aboard the ship is fine and, as Ludlow heads back to the airship to help, encourage them to focus on the Black Rayquaza. Ash, Liko and Roy call out to Rayquaza, telling it how it has inspired them to come this far and issue a challenge for it. After a moment, Rayquaza responds with a roar, accepting their challenge. Friede invites Dot to take part in the confrontation as well and divides them into teams, with him, Ash and Roy taking flight with Charizard and driving Rayquaza closer to the lighthouse. As Rayquaza moves towards them, Captain Pikachu uses Volt Tackle and creates a vortex that launches Sprigatito and Quaxly into the air, but Rayquaza easily swats them back down with its tail before they can attack.

Dot gets an idea, having Cap launch Sprigatito and Quaxly into the air again. Once in the air, Quaxly uses Low Kick to give Sprigatito a further boost as she uses Magical Leaf and Fuecoco, Pikachu and Charizard join in with their respective Flamethrowers and Thunderbolt. Rayquaza counters these attacks with Dragon Pulse, creating an explosion. Using the smoke as a cover, Charizard flies in closer, allowing Fuecoco and Pikachu to land a super effective Disarming Voice and Electroweb. However, the group's momentary celebration over the success of their maneuver quickly subsides as the smoke clears and Rayquaza roars, indicating that it is intending to fight seriously now. This becomes evident when Rayquaza launches a Draco Meteor, forcing Charizard to star making evasive maneuvers. Fuecoco falls off Charizard during these maneuvers, but Quaxly manages to save Fuecoco by slowing down his fall with Water Gun. Another Draco Meteor barrage quickly follows, knocking Quaxly out and leaving Terapagos in the path of a falling meteor. Liko rushes to defend Terapagos, but before the meteor can hit, it is suddenly sliced in half by Ceruledge, with Amethio entering the scene in its wake.

Ash: Oh great, he's here, what's next Team Rocket's gonna come back?

Annoyed that Spinel kept him out of the loop for this operation, Amethio declares that the Black Rayquaza will be his and pulls out out his Tera Orb, Terastallizing his Ceruledge into a pure Ghost type and having it attack Rayquaza with multiple boosted Phantom Forces. Friede understands that they have to team up in order to stand a chance against such an overwhelming opponent, so he too pulls out his Tera Orb, Terastallizes his Charizard, and has it use Tera Burst on Rayquaza.

Ash: We should terastallize too!

Pikachu: Pika pika!

Ash throws his Tera Orb towards Pikachu, but nothing happens

Ash: What?

Friede: Ash, did you terasallize before?

Ash: Yeah, when I was fighting Team Rocket when Liko Roy and I got that Wiglett food, oh no I didn't recharge the Tera Orb!

Fried: You knew that Tera Orbs need to be recharged?

Ash: Not excatly, Mega Stones, Z Crystals, Dnamax Bands, now Tera Orbs, they're different but share one common thing.

With Friede's help, Ash is able to recharge his Tera Orb, and Flying Tera Type Pikachu is back

Despite Amethio being irritated about Ash and Friede potentially getting in his way, he still lets them battle by his side as Charizard, Pikachu and Ceruledge attack Rayquaza together with many powerful attacks, leaving Liko, Roy, and their Pokémon amazed at the power of Terastallization. Just as Charizard, Pikachu and Ceruledge aim for a finishing blow, Rayquaza lets out a roar and dives into them with a devastating Dragon Ascent, forcing Friede and Amethio to recall their defeated partners, Ash cradling a defeated Pikachu.