I've done my fair share of the hostel circuit by now, in Europe, Scandinavia, South America, and now Asia. And I can safely say that Kaisu is my favorite. The name in Japanese is a play on the word "ocean," so the main space has this laid-back, surfer vibe, like you're in a bungalow somewhere. The owners rotate the art on the walls, and host performances such as local jazz musicians, so it carries a sense of creativity and invites you to linger even though there's all of Tokyo outside the door. The rooms are divided by gender, and each dorm has about 10 beds, but each person gets their own bunk "loft." That is, there's space in your bunk to keep all your things, so you kind of have a little room to yourself within the dorm, which is really nice for privacy and also for keeping your stuff out of everyone's way. Kaisu is also very clean, sleek, and peaceful. It's in Roppongi, which has many subway stations nearby as well as points of interest, so it's a no-brainer if you're in Tokyo and looking to save on an awesome stay.