I personally think half a day trip to Mt. Fuji area from Tokyo is not practical. The distance between Tokyo and Mt. Fuji area is around 120 km (75 miles) depending on where in Tokyo and where in Mt. Fuji area. Travel time alone will be close to two hours each way. Then all you do is have a meal where there is no guarantee of the view of Mt. Fuji. Mt. Fuji is often covered by cloud and view can be obstructed.