Nagisa first appeared in the first episode of the Eevee, Where Are You Going? shorts. It was exploring in the streets of a town, only to run foul of a Houndour when it stole its food. It managed to escape Houndour, and after seeing the ocean, it set sail on a boat. It reappeared in the second episode of the segment, where it fell off the boat. However, it was rescued by a Mantine, which took Eevee on its back so it could bring it to the shore.
In the third episode of the segment, Eevee and Mantine decided to try Mantine Surfing on a nearby wave. While it initially kept getting knocked off whenever Mantine did a flip, Eevee eventually learned how to time its jumps with Mantine's flips, allowing it to stay on Mantine's back. At the end of the fourth episode of the segment, Eevee arrived in Alola, where it said its farewells to Mantine and proceeded to explore the island. It first chased after a Wimpod before eating some Berries.
In the fifth episode of the segment, Eevee encountered Ash and his classmates' Pokémon for the first time and befriended them. In the sixth episode, Eevee played with them at the beach and even helped knock some Berries down from a tree to share with them. At sunset, the other Pokémon returned to their respective Trainers, while Eevee sadly returned to its impromptu home under a tree trunk to sleep.
In SM099, while wandering around Hau'oli City, Eevee ended up getting chased around by an AlolanPersian. Lana's Popplio saw its trouble and saved it, but soon after, they were spotted by Rapp, Zipp, and Tupp, who started fighting over Eevee. Ash and his classmates soon intervened, and during the ensuing battle, Popplio ended up learning Surf, giving Eevee a platform it could use to jump down from and send the Team Skull Grunts blasting off with a powerful Double-Edge. Seeing how good friends Popplio and Eevee had become, Lana's classmates encouraged her to catch Eevee. After a moment of thinking, she decided to name the Eevee Nagisa and asked if it wanted to come with her, which it gladly accepted. Lana then pulled out a Dive Ball from her pocket and caught Nagisa. When Lana later showed Nagisa to her family at her home, it turned out that her father had actually seen it surfing on Mantine in the third episode of Eevee, Where Are You Going?. Lana then gave Nagisa a haircut, getting rid of the hair that had been covering its eyes, much to its pleasure.
Personality and characteristics
Nagisa was shown to be adventurous and gluttonous, which often got it into trouble, such as when it ate a Houndour's food without permission, angering the Houndour into chasing it off. Nagisa is also shown to enjoy having fun, such as when it enjoyed falling into the ocean after falling off Mantine when it was Mantine Surfing. However, it was shown to be easily scared as well, such as when it ran from a Houndour and later when it found itself lost at sea.
Nagisa was shown to be playful towards new Pokémon, but also rather inconsiderate of their true feelings. In the fourth episode of the segment, it chased after a Wimpod despite it actually being scared. In the fifth episode of the segment, Nagisa cuddled a Pyukumuku, inadvertently angering it into attacking.
Nagisa and Popplio quickly became best friends after meeting each other. It even became friends with the Pokémon owned by its Trainer's friends. Nagisa quickly became loyal to Lana and bonded with her right away, after she help protect it from Team Skull.