According to reports out of Japan, the Shooto Middleweight Title is now VACANT. Previous champion Shinya Aoki vacated the title last Friday according to a report from BoutReview (in Japanese) and subsequently confirmed by Shooto in a blog post (blog.livedoor.jp/shooto_news). Aoki reigned since February '06 as champion but only made 1 defense. It seems he wants to focus more on fighting in other promotions and fighting at 70 kg (154 lbs).
It should also be noted, weight-wise, that the Middleweight division in Shooto is roughly equivalent to the Welterweight division in the Unified MMA rules except Shoot's MW division is 155-167.
I agree with his decision, especially if he has been facing pressure to defend. Now, more than ever, Aoki has to train his game completely, because his last loss was probably the most humbling he'll ever have. (by that I mean he was completely dominated by a fighter who refused to go even 80% on him)
Not really. Said defense he made was roughly 3 years ago, and as far as I know he's only fought in Shooto once the last couple years. And that was a non-title match. I wouldn't call it unprecedented though, Siyar Bahadurzada has held their Light Heavyweight Title (168-183) for nearly 3 years and never defended.