Familiars/Animal Sidekicks

So, I'm only putting this here because of Kilala, Sango's twin-tails friend/partner.

Mokona! Rabbit like creature as a sidekick character! Plus there's a character with "summons"

Another Isekai where the MC is a boy and enters the game only to look like a girl. He takes the job of a summoner with the sole focus of collecting cute monsters to fluff! So, yep lots of FLUFF!

A mage that drank the "eternal dew" freezes his age in time making him ageless (he's not immortal) and spends 5000 years study magic and many other things. When his familiar of 800 years (she also drank the same stuff) suggests the leave the dungeon they were currently in the story starts! MC's OP, but that's because he's lived for so long. If he hadn't he'd be a rather subpar guy. His familiar is a maxed out wolf named Pochi, and she's awesome! So fl

There are familiars and summons (that aren't human) so it counts

So I'm not a fan of this manga, but it fits the criteria so here it is. Fits because of the dog spirits.

A man dies after saving the pet cat, Mii, of a god and receives one favor. Asks to be revived in another world, with skills. But the cat, Mii, follows along so the god replaces the MC's skills to skills to take care of Mii. Mii is truly adorable, but I do feel a little sorry for the MC to have his survival skills replaced with cat pampering skills.

Doctor has a slime assistant. It's only a one shot, and man do I wish there was more!

Mythical creatures are real, and they need a doctor that can treat them. One MC is a werewolf (unknown to him) and he runs into MC 2 one day after transforming. MC 2 is a doctor that specializes in mythical creatures.

Kerberos is the reason I'm placing this here. He acts as both a sidekick and a familiar/teacher of sorts.

A boy is reincarnated as a prince and discovers he can have a summoned beast and starts on a journey to have one! He originally wants a cat, but his first summons turns out to be a mythical wolf! He does eventually get his cat, along with many other summons. Pure cuteness. Supposedly a sequel is coming, I'll keep an eye out for it.