He needs to contact a lawyer, or equivalent. Or maybe he can make arrangements with the Adventurers' Guild. Then, he can leave a big endowment for them to manage for the benefit of the Naoki Monster Research Institute.
The Institute could then hire assistants, and fund other monster researchers. Specific research could be funded by others, who would contribute to the endowment. For instance, any military power would benefit from understanding monsters better. They could then publish a Proceedings of the Naoki Institute, and have an annual meeting! It could become a model for other scientific research (e.g. a Magic Research Institute).