During July 2013 I spent a week exploring Izu Peninsula organised by Kiki Diving Club, which are based in Nakano, Tokyo. I visited a few different areas, the first being Arari Dive Centre on the west coast of Izu. This was a great spot for muck diving. I saw many Japanese pygmy pipehorses, tube blennies and nine different frogfish!
After Arari we headed to Osezaki, also on the west coast, and dived with Hamayuu Dive Centre for a couple of days. I
particularly liked the outside of the bay, where deepwater currents make for interesting diving beyond the 30m mark. Here we saw small schools of Cherry (Sacura margaritacea) and striped anthias (Pseudanthias fasciatus), both found only in deep water. Inside Osezaki bay is a proper muck dive, and very protected from currents and big seas. It is also a very popular site for learner divers and there can apparently be 100's of divers at the weekend, which I avoided like the plague!
Finally, Shingo (owner of Kiki Diving Club) and I visited Izu Oceanic Park on the east coast of the Izu peninsula. This is also a popular site and the critters' locations are well known to the management. They passed on the info and we succeeded in finding a few frogfish and some Japanese endemics. Unfortunately the swell picked up making entry/exit a bit of a nightmare, especially with a massive camera, so we just did two dives.