Prior to his introduction, Shigeru usually comes off as an arrogant show-off in the beginning. However, his personality begins to change as he matures. Later on in the series, he grows into a nicer and more humble person in both the anime and the video games. Throughout most of the series, he and Satoshi have an ongoing rivalry through most of the Kanto and Johto League sagas. However, this would soon diminish at later point. After his crushing defeat at the Indigo Plateau Pokemon League, his attitude towards Ash, who finished in the top sixteen far ahead of his rival, changes significantly after this turning point. His dealings with Pokemon seem to mature, as he starts travelling alone, wanting to better reestablish himself as a trainer.
His rivalry with Satoshi comes to a head at the Johto Leaue Silver Conference semi-finals, both trainers giving it their all, with Satoshi narrowly coming out the victor. After his lost, he then decides to no longer compete for the same goal as Satoshi, but instead dedicate his career into Pokemon research. Although no longer Satoshi's rival, he does tend to motivate Satoshi on ways of bettering himself as a trainer, at times scolding Satoshi when becoming overconfident over his wins particularly in the Orange League and Battle Frontier. In a sense, Shigeru is what urges Satoshi to start yet another new journey by traveling to the different regions across the world, such as Johto and Sinnoh. Despite his many absences in the series, Shigeru continues to remain a vital character, and one of Satoshi's most valued friends. He is bound to make more appearances during the Diamond and Pearl Saga, since he seems to have decided to be both a Pokémon trainer and a Pokémon researcher there. He guest-appears in episode forty-five of the Diamond and Pearl series helping to preserve a group of highly endangered Shieldon with Professor Rowan and his team.
Pokemon ( on hand )
Squirtle > Wartortle > Blastoise
Squirtle was the first Pokemon that Shigeru received, and has evolved into a Wartortle and then into Blastoise. It has never been removed from Shigeru’s active lineup and is his most powerful Pokemon, having defeated Satoshi’s Heracross and Bayleef. However, Blastoise was defeated by Satoshi’s Charizard despite having a clear Type advantage because Ash’s Charizard was more experienced. When Shigeru left on his new journey after the Johto League, he only took Blastoise with him, a gesture Satoshi would follow when leaving for Hoenn, only taking Pikachu and leaving the rest with Professor Oak. His Squirtle was seen only in a flashback in the episode "Challenge of the Samurai" while the Wartortle was never seen.
Doduo > Dodrio
Dodrio evolved from a Doduo that Shigeru had previously caught, and is one of the few Pokemon that he continued to carry with him after retiring from competition to become a Pokemon researcher.
Eevee > Umbreon
Umbreon evolved from Shigeru’s Eevee. Umbreon's main assets are its Agility, and it also seems to be Shigeru’s favorite Pokemon. In Episode 118, "The Rivalry Revival", Shigeru uses his Eevee in a battle against Satoshi's Pikachu. Takeshi remarks that the Eevee has bright eyes and a shiny coat of fur, revealing its high level of experience. Eevee ultimately defeated Pikachu, using a Take Down to knockout its opponent. Kenji noted that Shigeru 's Eevee was ready to evolve into a Stage-1 Pokemon, which happened before the events in Episode 173, "Power Play", in which Satoshi and his companions discover that the Eevee had evolved into an Umbreon.
Shigeru used it to battle Satoshi's Pikachu in the final episode of Pokemon: Battle Frontier "Home Is Where The Start Is", defeating Pikachu with a powerful Thunder Punch.