Today on an NHK Education show called "Runrun", they analyzed idol culture and business.
https://www.bilibili.com/video/av34273388The show classified Morning Musume as a "high class or luxury brand" (Kyokyuu). Their brand equity strategy is the graduating and joining the group strategy. They continued this strategy for 20 years and maintained their top 10 65 singles status on Oricon. If you hear their group name, you instantly knew their brand.
They also mentioned if they had a business model for idols, to them it would be :
Morning Musume = Toyota and Nissan. Morning Musume uses a car manufacturer "full line strategy" to describe their group lineup management.
AKB48 = Japanet Takata ジャパネットたかた (late night infomercial shopping channel company)
AKB48 uses a PCDA cycle strategy for marketing. Advertising company Dentsu business model is (PCDA) Plan-Do-Check-Act.