Who can tell me the story of Lu Xun’s anonymous letter?

Lu Xun studied medicine in Japan. At that time, the results of Chinese students studying abroad were very poor, and few passed the exam. Lu Xun often asked his teacher, Mr. Fujino, for advice. Mr. Fujino taught him wholeheartedly, guided him many times on his notes, and left many underlines and red circles. This is understandable. Lu Xun passed all the exams this school year, and his grades in several subjects were quite high, reaching scores in the 80s and 90s. This made the Japanese classmate very unhappy and suspected that Mr. Fujino revealed the title in Lu Xun’s notes. They wrote a letter to Lu Xun, which began with "Repent!" This is a word from the Bible, which means that Lu Xun made a big mistake. In addition, he often made sarcastic remarks and insinuations about Lu Xun. That's the general idea.