At Saitama's Honda Airport, why not try skydiving? You can with Tokyo Skydiving Club. At 3,800 metres above ground and higher than Mount Fuji, I was a little nervous but the worst part, as you begin to fall, lasts just a fraction of a second.
During the freefall, it felt like I was truly flying and was an amazing experience overall. I hope to try skydiving again in many different places.
Tokyo Skydiving Club (Japanese)