Last year me and another two friends went to Tokyo for 4 days. We were staying in New Zealand at that time, so best way to fly to Japan is through Gold Coast, Australia.
Depart from Gold Coast airport using Jetstar to Narita on December 1 and return on December 6. Return trip cost RM2000 per person. Brought 60k yen and only spent 50k yen. Stay at K house hostel which is pretty cheap, 3.2k yen per night for our three bed bedroom. Honestly, 5 days in Tokyo is just not enough but if you plan properly then it should be fine.