Who: Posuposu Otani (ポスポス大谷）
What: Accordian and throat singing
Link: Posuposu myspace
I'm sure some people read the words "throat singing" and immediately tune out which is fair enough. It had its time as a kind of world music fad, and maybe one too many hippies learnt the technique and wore it out.
But give posuposu a chance: for the most part he uses his throat singing powers sparely and for good not evil. In one of his many eccentric touches, he will usually say the word "posuposu" before he launches into a throat-singing chorus so you always have ample warning. His normal singing voice is also pretty odd, and he's been known to break out a Jews harp, so if you're not a fan of warbling, you might not have much respite.
Posuposu's songs' subject matter is various, but often centers on UFOs. In my personal favourite posuposu song, he exhorts aliens to show him how to use their mysterious powers. He also has a fondness for puns as he explains (in English) at the start of this youtube clip. (The clip is from a performance at Koenji's 無力無善寺 (mu-ryoku muzenji) live house last year).
Posuposu is my favourite kind of eccentric: he takes a bunch of disparate things that he enjoys and throws them together in his performances. There is no hint of put-on oddness which is what sometimes passes for experimental in Tokyo.