Being what is essentially a babysitter to an angry pair of land and sea gods can get tiring for poor Rayquaza, so within the privacy that high altitudes provide, it no longer has to care for anyone but itself. Both people and other pokemon may think it's intimidating but deep down it just wants to be free of responsibilities, even for just a bit. Thankfully a certain, puffy human invention helps it relax quite a bit...
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I had this one in mind for a long time. Definitely not an easy pokemon to diaper, but just giving it legs makes the whole process easier. If you're wondering why the legs look kinda like its arms, it's because I felt it fit since eastern dragons tend to have their arms and legs indistinguishable form one another (and I'd imagine it'd be easier for Rayquaza to move on the ground if it had more than 1 set of limbs.)

(Day 26: Gen 3 Legendary)