If 19th Tera type suppose to be like G-max factor than then that might explain Ash's Pikachu's 10 million bolt Thunderbolt. Maybe Ash's Pikachu also has 19th Tera type that influence its Z-crystal and turned it into a special Z-move where Pikachu shoot Rainbow Colored Thunderbolt.
https://twitter.com/ThePokeRaf/status/1705143898924871935Specially where the Rainbow Light that entering Terapagos shell resemble Pikachu's 10 million bolt.
