近藤ひさし (Kondo Hisashi) is YUI's musical producer. They have been working together since YUI's early begginings.
He is the host of a radio show called 近藤ひさし・サタデー☆ヤングナイト（サタ☆ヤン） (Hisashi Kondo Saturday Young Night) or "Satayan"
He is also recognized as "YUI LOVER Hero" for taking moe moe kyun pictures of YUI even when he's not allowed to do so, and for always tease YUI about the lack of updates in her diary.

Profile
Name: 近藤ひさし / HISASHI KONDO
Date of birth: April 14th, 1969
Blood type: O
Birthplace: Hokkaido

External Links

Hisashi Kondo's blog http://ameblo.jp/hisashikondo/
Older blog http://sound.jp/rock-hisashi/
Satayan website http://www.air-g.co.jp/hisashi/
Satayan encore podcast http://www.monoglobe.jp/podcasting/saturdayyoung_night.html
Honeybee Studio http://honeybeestudio.jp/
Profile at Spotlight Magazine http://spotlight-magazine.jp/hisashikondo/profile.html