I discovered this single by Tokyo Ska Paradise Orchestra（東京スカパラダイスオーケストラ）some weeks ago titled "Tsuioku no Lilac" (Lilacs of Reminiscence) that came out back in December 2005.
With the smooth stylings of Hanaregumi（ハナレグミ）as the guest vocalist, TSPO's 28th single still had the band's usual cool ska strut, but there seemed to be a bit more of a subdued feeling to the arrangement. Plus, despite Hanaregumi's high-toned delivery, the video itself was done in a more solemn tone with the band members all sporting dark suits and countenances while playing in a more dimly-lit setting.
I was reading some of the comments underneath this YouTube video, and apparently the song created by baritone saxophonist Atsushi Yanaka（谷中敦）and keyboardist Yuuichi Oki（沖祐市）was meant to be a tribute to a former member of Tokyo Sky Paradise Orchestra who had passed away. I did some checking about that, and I found out that vocalist Cleanhead Gimura（クリーンヘッド・ギムラ）and drummer Tatsuyuki Aoki（青木達之）had died in the 1990s, both at the age of 32. Perhaps the song, as the title hints at, was made as a memorial to Gimura and Aoki.
"Tsuioku no Lilac" peaked at No. 23 on Oricon. It was also a track on the band's 12th album "Wild Peace" which came out in June 2006 that went as high as No. 2 on the charts.