As a kid, I always loved Kaiju and the superheroes who changed size to fight them. Let’s make a monk who does that.
Be careful when you fight monsters, lest you become one. As a kaiju slayer, you have been trained to harness power in yourself and use it to attack the monsters who threaten your people.
Starting when you choose this tradition at 3rd level, you can manipulate yourself using ki. You can spend a ki point to increase your size, spending one ki point per size increased as a bonus action. All objects you hold, wear, and wield increase in size as well. Your unarmed damage increases as well, with each size increase modifying your damage by one step along this track. 1d4->1d6->1d8->1d10->2d6->2d8->2d10->2d12. This size may be maintained for up to one hour, but you may end it at any time as a reaction.
At 6th level, you learn how to fight those smaller than yourself. For each size category that you are larger than an enemy gain a +1 bonus to damage against that target.
Beginning at 11th level, you learn to harness the abilities of the monsters you fight. For each size category you increase your size, you gain a +1 bonus to your AC.
At 17th level, you gain the ability to fully harness your kaiju power. For each size category you increase yourself, increase your proficiency bonus for all weapon and unarmed attacks by +1.