Who: Sei and Jun-ichirou Tanaka(田中淳一郎)
What: Avant "pop"
Web: ju sei's webpage
From my outsider perspective, ju sei are the "it" duo of Tokyo improv/weirdo music at the moment. Their music is a combination of pop, genuine improvisation, electronica and just plain oddness, although it always feels well thought out. Jun holds down the fort with his tightly controlled guitar and effects constructions and Sei brings the alien charm, her vocals anchored by a precise pop delivery, but often careening off into screaming, squealing, or Ami Yoshida-esque frothiness. The ju sei set-list includes enough straight up sing-along hits to keep the average listener happy, while the weird detours have the Tokyo noise hipsters nodding subtly in appreciation.
One interesting part of ju sei's recent story (they've been making music for the better part of 10 years I believe) is how the attention of a foreigner in Tokyo - the remarkable Mr Anthony Guerra - helped bring them to greater prominence, at least in the Tokyo odd music scene. Anthony's black petal label (see the link from his name) is still only place to get an official ju sei release (although Enban has released a DVD of all of their instore performances). According to ju sei's web page, a new album will finally be available this spring.
Sei and Jun have a variety of side projects including shining rice (ju sei + Anthony Guerra), Chikara (a Jun-lead ensemble with an ever changing line-up), and Sei can be found MCing in her cold, formal Japanese announcer style (imagine an announcement on the shinkansen) at many an Enban linked event. As a duo, they have also been performing with 宇波拓(Taku Unami)'s absurd lounge act Hose a lot recently.
Unfotunately, it's hard to track down any ju sei perfomances on-line, probably partially because the word ju sei has a few dramatic meanings in Japanese ("gunshot", "brutality", "multiple stars" !) so it's relatively common as a tag on the web. If you know of any videos, let me know and I'll link to them here.