Gomi Gojo's Territory Opening Gesture was an important element in the " Return of Curse ". Gotto Gojo's domain was displayed as 'Boundless Empty'. This gesture was to pull the enemy into the infinite inner side, forcing the enemy's brain to produce a large amount of information, causing the brain to lose its function and could only stand and wait for death. Although there was no specific description of the hand gesture, it could be speculated that the hand gesture was to expand the domain through a specific posture of the hands.
Yes, you can. Since you can use public domain stories freely, you can create products or services based on them and then sell them. For example, you could write a novel based on a public domain story and sell it. Just make sure you follow all the legal requirements and ethical norms while doing so.
Firstly, set your writing goal as promoting positive values. Then, use more general and positive descriptive words. For example, if you want to describe a character's physical state, you can use words like 'gentle movement' instead of something sexualized. And always be aware of the ethical boundaries in writing.
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.