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.
The recognition of the seal character seal could be achieved by using the seal mouse recognition app. First, he clicked on the mouse recognition app on his phone's desktop. Then, he chose the first option of "Picture Identification" in the Zhuan Shu app. After entering the next step, he chose "Take a Picture" or select a picture to identify. The software would automatically recognize the simplified Chinese characters corresponding to the seal characters in the picture.