Character creation and writing out cutscenes are my favorite part about making an RPG! Building the world, writing interactions, having a splash of lore even if the game is super short... and of course, whilst testing a game can have some unfun aspects about it, I enjoy testing cutscenes over and over to hear the voice acting applied!
Parts that are my least favorite definitely has to be setting walking routes when eventing (lots of counting squares on the grid), cutting voiced lines 'cause it's so tedious... leveling the voices isn't so bad, since in RM, I can do that in internally rather than externally, which I usually do in my VNs on another engine. BUT! Since voice over is lower and the default audio is always SUPER LOUD, the part I really, really dislike the most when doing a new RPG is internally leveling all the game sounds I am going to be using. All the system sounds, specified animations I will use a lot (gets really tedious when dealing with which animations are used in what skills, etc.) Ugh.... that's the most painful part in my opinion. Luckily I was smart with my one map challenge project, lowering everything beforehand, so when I added voices to the build later, I could just focus on voice leveling and ignore SFX for once lol.
That aside, overall, I love the game making experience, even the longsuffering of the boring and tedious parts, because when your game is done, you feel so accomplished!