Shakuhachi applied oil to the surface of the bamboo to maintain it and prevent it from cracking due to drying. Plant oil could be used, such as natural tea oil, olive oil, or walnut oil. After applying a small amount of oil and wiping it clean, it formed a thin layer of oil film. However, the search results did not specify which part of the shakuhachi should be oiled. Therefore, I don't know where Shakuhachi applied the oil.
The four types of weight-loss vegetables that were the most oily were winter melons, tomatoes, cucumbers, and celery. The fat content of winter melon was zero, while the ingredients in other vegetables could suppress fat production and have the effect of scraping oil. Tomatoes were rich in nutritional fiber and pectins, which helped to loosen the intestines and relieve the bowels, accelerate the movement of the intestines and stomach, and was good for scraping oil. Cucumbers could increase satiety, eliminate excess garbage, prevent fat absorption, and help to scrape oil. Celery is rich in dietary-fiber, which can promote digestive activity and reduce fat absorption. These vegetables were suitable for people who wanted to lose weight.
Toge Inumaki is important too. His special cursed speech ability makes him stand out. Also, the principal of the school, Masamichi Yaga, is likely to be important as he is in a position of authority and has an influence on Gojo and the other students. There could be other characters like the members of different clans that also play roles in the complex web of the story.