After Miku Append began, Rin and Len (鏡音リン・レン・アペンド) were confirmed to have appends being worked on.
On the 17th of August, work began on Rin's "Sweet" append.[16] On the 18th, it was announced that construction of the Len Append α had completed and with help of the main Kagamine fans public testing would begin in the next few weeks.[17] A series of "soft" β samples would be shown.[18] On the 20th of August, Wat reported work had began on a "Len_soft" vocal.[19]
There was indecisiveness on if one of Len's Append would end up as "Power" or "solid".[2