Abstract: The article presents an English translation of the Japan vs. Shimizu decision (信玄 公 旗 掛 松 事件 Shingen-kō hata kake matsu jiken), which is a central court decision in the history of Japanese civil law. With its decision in a tort law dispute over a historically significant tree, the Japanese Imperial Court of Justice has set a legal precedent for taking into account the principle of good faith. Lawsuits based on an "improper exercise of law" (権 利 の 濫用 kenri no ran'yō) have since played a major role in tort, contract and property law in Japan. The authors give an overview of the background of the case and discuss the legal and dogmatic significance of the decision, for which they reconstruct the historical facts and the process flow. In this way, they hope to expose an important area of Japanese law.