It may be too late for you, but Shibuya is the new bass heaven, not Ochanomizu.
Try the Kurosawa Shibuya Bass Center, Ikebe, ESP, Ishibashi, Hoochies,
I live in Shibuya, so temptation is around me all the time.
If you go to Ochanomizu, go to the Kurosawa Ochanomizu Bass Center and Main Street Guitars.