Nagisa's best friend might be really surprised at first. But then, being a true friend, would support Nagisa through this strange change. They would probably help Nagisa with things like choosing girl - appropriate clothes or dealing with any mean comments from other students.
Kayano would be completely devastated. Since she had a special bond with Nagisa, she might become withdrawn and filled with rage, vowing to take revenge on whoever was responsible.
Their other classmates like Okuda would be very sweet. She might make them some special potions or concoctions as wedding gifts, something that symbolizes good luck and a long - lasting marriage. And she would be all shy and cute about presenting it to them.
Some students might be in awe of him. His demigod status and the stories he could tell about fighting monsters would be really cool to them. Others might be a bit jealous, especially those who pride themselves on being pure - blood wizards and think their magic is superior. But then there would be those who would be friendly and curious, like the Weasley twins. They would probably want to team up with him to pull some epic pranks using his unique skills.
It could be that a teacher or another adult mentions it during a class discussion. That might pique the interest of the E class and they start digging deeper.
Among Fan Xian's students, the one who betrayed him was Hou Jichang. Hou Jichang initially followed Fan Xian not because of admiration or admiration, but for his own interests and future. However, when Fan Xian encountered difficulties, Hou Jichang immediately defected to Fan Xian's opponent and helped his opponent plot against Fan Xian.