These two OVA’s are based on the adult manga by Midori no Ruupe. The timeline in the two OVA’s intertwines. First when both OVA’s are watched is the whole story revealed.
The stepchildren Ichina and Imako used to live under the same roof, just like brother and sister. However, the intimacy of sex, which started with innocent interest, distorts the relationship between the two.
1 - 1Imako System Episode 1 Feb. 28, 2014
1 - 2Imako System Episode 2 May. 30, 2014