The Belle II is a high-energy physics experiment with e+e- collision using the SuperKEKB collider at KEK, Japan. The main goal of Belle II is to search for New Physics beyond the Standard Model and probe the dark sector. By tagging the full decay chain of one of the B mesons, we can study the signal B decay mode, even with invisible particles in the final state. Belle II has developed the Full Event Interpretation (FEI) that is an exclusive tagging algorithm of B mesons using the Boosted Decision Tree (BDT) for training classifiers. In this presentation, we explain FEI and also present some example analyses in which FEI has been extensively applied.