Japan has quite distinct seasons - cold and snowy in winter, hot and sweaty in summer - so not everywhere is in condition at once. Mid-August you'd want to go high ... the granite at Ogawayama, for example. Mitake, which gets a lot of press because it is close to Tokyo, would be horrendous mid-summer but good in winter.
The Japanese grading system borrows its method from martial arts. It is split into two tiers: Kyu and Dan. The beginner's tier is Kyu - ranging from the easiest at 10-Kyu up to the hardest at 1-Kyu (roughly 6C+7A or V5/6). The expert tier is Dan - ranging from the easiest at 1-Dan - known as Shodan - (roughly 7A+/B or V7/8) up to the current hardest which is 6-Dan (8C+ or V16).
Komiyama (古美山) Edit
A small area of limestone/chert boulders, centred around the Tama river, two hours north of Tokyo. Attractive surroundings, but limited bouldering.
Mitake is about 90 minutes on the chuo-line train due west from Shinjuku - the massive insane station on the west side of Tokyo. The guys at the climbing wall had told me I could rent a pad from the convenience store in Mitake just over the bridge from the station. The store was pretty empty, a few sad packets of biscuits and some beer in the fridge - but strangely did have some bouldering pads. A few shouts of 'sumimasen' and a guy popped in from next door. I got a large fat newish metolius pad for the day. Â£4 (1000 yen). The guy didn't even want a deposit. The river is beautiful: fast flowing clear blue-green water. Admittedly, quite a lot of ramblers and fishermen but a gloriously long way from the daily insanity of Tokyo. Some guys were warming up on the first set of blocs, nods were exchanged and I wandered over to have a go. The bouldering is pretty small scale - I'd say five spots along the river that are ok, each with one or maybe two decent blocs. The in-between problems look like nothing more than fillers, some on pretty damn small boulders. It takes only 15 mins or so to walk end to end, all the problems shown in the guide. They are spread about equally up and down stream of the bridge, on both sides of the river but there are several convenient bridges to cross over. The polish is rivalled only by the likes of minus ten: river-worn granite (I think - my appreciation of geology is appalling) plus a lot of traffic. However, given the small number of blocs, there's a cool variety of styles, desperate near-frictionless rounded grovelling and pedalling up little slabs, and some steeper crimpy body tension problems. The area's centre piece is the (v. rough translation) "ninja can't climb" bloc which is a respectable size and kicks off at about Font7a. If only there had been enough mats I would have jumped on to show up the locals (see photo)! All in all, a great escape from the city. The blocs are in a beautiful setting; sitting by the river is already worth the day trip. Although it was fairly busy on a sunny saturday, the locals were really friendly, very encouraging and amused both by my attempts to climb and to speak japanese; I displayed about equal ability in each discipline... It is by no means a world class venue, but cheap and easy to get to from Tokyo, and a nice change from the gym.
Overview taken from this thread, which contains more info and pics.
Mitsumine is a small but excellent area near Tokyo. It has a good circuit which isn't too hard and a couple of classic problems. There are a couple of harder problems, including an 8A crack (!) and a wall marked as a project in the guide, which looks brick but do-able (might post a pic of this later).
It's relatively easy to get there by public transport from Tokyo. From Ikebukuro station in Tokyo, take the Seibu line to Chichibu. An express train takes about 90mins and costs Y1500. A short walk from the Seibu Chichibu station is the Tetsudo line station, where you can catch a train to Mitsumine-guchi (25 mins, about Y400). From here catch a bus from the station direction Chichibu-ko and get off at the third stop outside a primary school (15mins, about Y350). Check the last bus times when you get off. Head down the steep bank towards the river and the boulders are obvious.
I went in the middle of April and it was getting pretty hot. The rock is a beautiful smooth schist with some very sculptural blocks. I went on a weekday and had the place to myself, apart from the resident macaques...
Overview taken from this post, which contains more infor and pics.
Possibly the biggest area in Japan. Two and a half hours southwest of Tokyo. Lots of pockets and slopers, but very few crimps.
Okyojō (大給城) Edit
Super hard roof climbing.