For me...should be no problem to travel during that period . Its only recommendation ,its up to you. 

kingofrave89 please clarify what you mean by "and Fuji" if you want better advice. Do you mean you want to climb Mount Fuji? Or do you mean the Fuji five lakes area? Or do you mean go Hakone or some other onsen / relax area with a view of mt fuji?

These are main holidays in Japan where everyone in Japan will travel out or balik kampung. In this long period there will be one or two days where shinkansen will fill up until no room for standing. Also everywhere you go there will be a lot of people and hotels tend to be more expensive. Hence this is the issue I face as well. I will also be on holiday and to balik Malaysia, ticket cost 2-3 times more!

May I add - avoid new year too! Most establishment closed on 1/1 ,hotel rates almost rack rate, and long distance travel via shinkansen also fully booked unless u willing to stand on none reserved coaches....well from my recent new year experience there

Get ready to feel oven heat sensation.
Tokyo summer avg temperature are 34 -38 Celsius.
Must bring umbrella and UV protection stuff.

Must go Enoshima beach. Full of bikini girls now.
How to go Enoshima can refer to Page 1

Check your electric appliances input voltage..for laptop or AC to DC power supplies,usually no need 110v-to-230v transformer
But if for those hair dryer and stuff,u need the transformer

Sorry hope i can busybody and answer. For me i use just the international adapter for charger mainly for laptop and phones. All still alive. I believe only if you want to bring back japanaese appliances to use in malaysia then you need tgose converters. And those got different types but thats another thread

Malaysia Electronic device have no problem at Japan. No need any voltage converter. Only need was socket Head plug converter only.
Malaysia electronic device adapter are 230 Voltage design while Japan only used 110V.

But if you buy Japan electronic back to Malaysia then you need converter + Step down adapter. Japan Adapter only 110V. If plug into Malaysia socket. with 1 sec Malaysia 230V will ''goreng'' the adapter + electronic device.

One Hakone loop need take one whole day already.
Enoshima + Kamakura are one full day
Lake Kawaguchi + Gotemba are one full day.

I have used it for my trip to Japan this March. My review, speed is good and coverage is good as well. most of the time I can get with full speed except arashiyama, but its considerable okay since its mountain area. However, I would recommend you to get the router from them one or two day earlier before your departure. During my trip, they havent open their counter in KLIA2 yet. So, I have to wait for them to pass me the router and somehow they only reach KLIA2 one hour before my flight. Frightened me out as I thought I almost couldnt make it to my plane. BTW, their main office is around KLCC, so if you happen to be working nearby, then might as well get the router from the main office.