@taiyo I worked there. It was largely inspired from Friendster according to https://enterprise.watch.impress.co.jp/cda/web2/2006/05/30/7858.html.
Speaking of search, it was working okay, from my perspective and sadly used to find problematic/controversial users.
https://news.livedoor.com/article/detail/3424175/
> 『mixi』の検索機能を使い、他人の日記を検索することができる。この機能をもちいて“万引き”“無免許”“飲酒”“俺の正体はドナルド”などと、ありがちなワードを根気よく検索すれば、それなりのヤバイ日記がみつかるのだ。