A medieval world where mankind is surrounded by sauropod sized creatures
Even the smallest village need to build wood fortification to keep them out, or to have their own trained beast for defence, typically herbivore ones.
Raising and training such creatures are critical for kingdoms as they are big enough that no human-based anti-cavalry unit can counter them (horse don't even exist)
Being able to taming big carnivorous sauropod make you akin to nobility

The story would be about tamers who end up working together to protect a princess from her uncle, who is trying to kill her to become the ascendant royal lineage.
Working together is made difficult, one of the MCs beast is the greatest carnivore to exist (he's named Fluffy), another is the biggest herbivore to exist (she's named Breakalot), another is a flying mount who need room to take off (he's named Fishy), another is a charging herbivore (Ramalot), last one is a giant mammal wolf (Sniffy).