Shigeru is full of doubts and of awareness of his own mistakes, failures and insufficiencies. It is something that was hinted pretty early when he decided to leave and encouraged others to do the same, when he faced the fact that he wouldn’t be able to do anything about the Digda in EP031. It then resurfaced occasionally when losses (Pokémon battles, hesitations about his future and path, inability to be what (he thought) he was expected to be) were more explicit and perceived as such.
Shigeru knows how to play with language. It has been shown since the first episode, in which his toying with Satoshi established a distance through the use of honorifics: to Satoshi’s implied proximity (Satoshi just called him “Shigeru”), Shigeru demanded that he add the -kun and himself switched between -kun and -san towards Satoshi. He covered a factual pre-existing relationship with a veil, created by words, to deny its consequences. He twisted reality with abstractions. “Friends” was never pronounced: to Satoshi’s genuinely friendly and curious behaviour, Shigeru opposed the word “rival” (in English), something that Satoshi discovered at that moment (and complied with, as he reminded Shigeru in EP018 that they were supposed to be that). When the word osananajimi (“Childhood friends”) was used for the first time, it was in Satoshi’s mouth and way later (EP268). However, it was something that could have been expected given Red and Green’s status in that regard in the games.
But Shigeru manages to push it back so efficiently with words that it had never been brought up before that.
Shigeru’s behaviour is the same: it was often presented as a game of pretense. Of course, there were the flamboyant, exuberant, bratty and petty demonstrations at the beginning (Shigeru creating his own legend, always being marked by exaggerations); but it somehow remained after downfalls: Shigeru kept his expressions hidden from Satoshi when defeated.
Was his defeat at the Johto league a loss? A lot of things (this smile and the following ones, him being able to confess that he wanted to quit competitive training, something that seemed to have been nagging him for a while, sufficiently for Ookido to notice he wasn’t happy while receiving his Hoenn dex) showed it was more of a relief.
We don’t know a lot about Shigeru’s travels, about his way of thinking. There were, however, mirrored details that could help trace what happened in him since the Tokiwa Gym: the first round of the gym (which he won) being re-enacted at the Kanto league (where he lost),
the evolution of Eievui into Blacky (a Dark type, which is immune to Psychic types),
the fact that Shigeru’s tendency to be consistently illuminated had morphed into him being characterized by night after having been kept in the Tokiwa Gym’s shadows before Satoshi’s arrival, the fact that, with Ptera and then the Tatetops, he was hinted to specialize in ancient, disappeared Pokémon (so unknown to the modern knowledge),
were giving the impression that Shigeru, consciously or not, was haunted by this particular loss.
Shigeru seems to often put on a facade or, at least, to choose what he wants to show of himself. He was insecure about his skills (SS015) and accepted to show it to Kenji and Ookido; but as soon as he was face to face with Satoshi again (AG192), he took back a confident and nearly authoritative attitude that somehow made Satoshi somehow chase after him, or at least in the same direction – Shigeru was leaving without a sign, leaving for Sinnoh, and Satoshi decided to do the same right away.
There were two big instances of Shigeru accepting to open up to him: the successive talks around the lake during the Johto league (Shigeru thinking about the past and how it had influenced their present), and in Sinnoh (when Shigeru took the blame of Tatetops’ kidnapping, because he wasn’t able to notice its fatigue).
His behaviour fluctuates a lot around Satoshi – it is often a matter of what he wants to show in the first place and what influence he seeks to have on Satoshi (drowning him in his condescendence, making him move forwards). Moments in which he confided have been rare, but it doesn’t mean that Shigeru doesn’t care about Satoshi’s opinion, well-being or dynamism.
Am I the only one to have the feeling that his strictness (to make sure that Satoshi would follow a new road) at the end of Advanced Generation was a way to try to apologize?