Brock takes care of ten siblings when his parents hit the road. This also extends to Ash and Misty and will give them big bro help and advice when they need it.
Practically every Pokémon on Ash's team was this to Togepi. In particular, when a Raichu zapped Togepi along with Pikachu in the Pikachu's Vacation short, that was what made Pikachu angry enough to fight back against it.
May has a big sister instinct towards her little brother Max, to the point where she is willing to sacrifice her contest dreams to make sure he's safe.
She once teamed up with Gym Leader Liza when Max and Tate (their respective little brothers) got captured on a rocket by Team Rocket. They utterly destroyed them.
Since May's introduction, Ash tends to have this with most of his female companions due to taking his place as the novice trainer. Possibly inverted since Ash will never be more than a slightly older ten at best.
Similarly Pikachu often plays this to all of the team's newer Pokémon, especially the younger or un-evolved ones. Secondary mascots of the team such as Togepi, Piplup, Axew and Dedenne especially are the target of Pikachu's softer protective side.
Hawlucha is fiercely protective of Noibat, who utterly adores the older Pokémon. This winds up being turned around when Noibat evolves into Noivern to save an injured Hawlucha from a dangerous fall.
Gladion, while aloof at first, is shown to to be fiercely protective of his sister Lillie after her tramatic encounter with an Ultra Beast, and is willing to risk his own life to make sure she's safe. Type: Null/Silvally proves to have a similar desire to protect the second time around.
Kiawe has this to comically melodramatic levels towards his little sister Mimo. He later becomes Big Brother Mentor to Ash and Sophocles.
Kiawe's Turtonator is noted at one point as having a "big brother" demeanour as well. He willingly joined Kiawe after he helped Turtonator protect some Pokémon from a menacing Crawdaunt. He routinely helps other Pokémon train and master attacks (particularly Litten and later Vikavolt), and at one point made a Diving Save to protect Mimo from a Thunder attack without Kiawe's command.
In Pokémon Adventures, much like his anime counterpart, Gladion cares for Lillie greatly, and he and Type: Null jumped to the rescue to save her from an attacking Guzzlord.
Leon gets this in Journeys during the Sword & Shield Arc when he shields Ash and Goh from Eternatus exploding out of his Pokeball. Despite being badly injured, he still tries to get up and protect the two ten year olds.
