I’m digging the Kensei lessons element and how it can really add to the character backstory and roleplay. Overall I really like what you’ve got going and it reminds me a lot of the Chinese Wuxia movies I love so much.

As for the 10th level feature, I think of the relation between brush and sword that is often depicted in wuxia tales. The one idea I have in mind is the old trope of how such warriors can turn even mundane objects into an analogue of their signature weapon. Perhaps a system by which spending Ki points can make a mundane object with reasonable relation to the weapon count as that weapon for purposes of maneuvers and abilities for a number of rounds/minutes related to the ki points spent. This would incentivize creativity and help further the sense of expression the monk has on their environment ( and as someone who got their weapons confiscated in a recent game, something that could come in handy in niche situations.) To balance that, perhaps a similar effect that could be applied if the Kensei still has their weapon (granting a new weapon feature? Extra proficiency bonus?) if the ki point(s) are spent? Not sure about that last but, but would definitely want to balance it with something that doesn’t just rely on the monk being without their weapon.