Toshiya Kawai is working on both physical and mathematical aspects of quantum field theory and string theory. He likes algebraic and enumerative approaches to these subjects preferably with relevance to geometrical problems. Over the last years he has been studying string duality phenomena. These dualities predict interesting correspondences between seemingly disparate geometric objects. In particular there are interesting relations between physics and enumerative geometry of Calabi-Yau manifolds. Some key words of his current research are: 2d CFT, Gromov-Witten invariants and their reformulation in terms of brane counting, elliptic genus and elliptic cohomology, Jacobi forms, Borcherds products.