In this paper, we present a serious game that can prevent elderly people from brain illness using natural finger interaction and Fumanet exercise. As population of elderly people has continually grown in our society, brain illness like dementia can be naturally observed, which makes treatment cost up rapidly. Hence, we propose Leap-Motion based serious game for elderly people, which uses natural finger motions to interact with game contents. In our approach, we enhance finger motion recognition rate by adding auxiliary conditions that is superior to ordinary Leap-Motion APIs. Finally, we have also carried out user study and quantitative analysis to verify our methods.