A tremor is an involuntary rhythmic shaking movement of the muscles, which reduces the precision of hand and finger movements. It is difficult for individuals with hand tremors to type accurately using small- and high-density targets, such as keyboard. This research proposes an optical see-through mixed reality system that reduces hand tremors so that the individual can type steadily. The system virtually stabilizes the individual’s hand tremors by optically overlapping the trembling hand with a stabilized virtual hand to produce a realistic typing sensation without any tremors. The simulation experiments proved that the system supports trembling hand typing. By comprehensively investigating both the objective (time and error ratios) and the subjective (the sense of ownership, agency, and pertinence) aspects, the system with a virtual:real intensity ratio of 0.75:0.25 was found to be optimal.