I've been making a TAS of this game for fun and just finished the first 6 levels, it's not perfect but still gives a good idea what a very fast speedrun would look like. While doing this, I've found the following tech [with possible RTA viability in brackets]:

• Kicking mid-air preserves your speed for the duration of the kick animation. By kicking near the end of long jumps and double jumps, we go slightly faster throughout the run. You can also kick immediately after jumping from a swing for extra speed. [Surely doable with practice. You have several frames towards the end of a long jump where kicking keeps the speed for longer than usual.]

• Kicking while long jumping shifts Kim in the direction you're moving. Can be used to clip into platforms and snap up onto them. [Seems to be fairly lenient RTA: if you're long jumping into the side of a platform but not moving, kicking should snap you onto it.]

• Falling onto the corner of a ledge in the right spot can make the game think Kim is on the ground and let you jump normally. [Already happens a lot in the current RTA record, so it's certainly doable.]

• Kicking on the frame that you land from a long fall cancels the lengthy landing animation. [1 frame window, given the speed at which you're usually falling to get the long animation, likely not RTA viable but you don't get punished for missing it so you may as well go for it.]

Also side note, Rufus moves a bit faster in the air than on the ground, so constantly jumping in the mole rat sections saves time over just running.