On 13th May 2015, an update on the official website of Shizukaze and Kizuna announced that all members will “graduate” in summer 2015.
The reason for the concurrent graduation was cited to be due to the girls’ self-admitted difficulty in the upkeep of their idol commitments as they transition from teenage girls to young members of the society. Although the formal term used in the announcement is “graduation”, there is no mention of attempts to recruit new members to replace the graduates, thus this “graduation” can essentially be seen as the group’s disbandment.
At the point in time during the announcement, one of the members, Haruko Mizuno, had already graduated earlier in May due to poor health and will be retiring from the entertainment industry entirely. According to idol news site jpop-idols.com, her leaving prompted the other members to graduate.
The official disbandment date will be released on a later date, and there are currently no explicit plans for a farewell performance or the like.
The unit was originally formed as a combination of the idol groups Shizukaze and Kizuna formed in 2009 and 2010 respectively. They were signed under the label T-Palette Records in 2011.
Source: Tokyo Girls Update, Pure Idol Heart, jpopidols.com