Casimir II was the son of Bogislaw I and Anastasia, a daughter of the Polish duke Mieszko III.

As Casimir still was a minor in 1187, his mother Anastasia ruled in his place until 1194 as well as, until 1189, the Swantiboride Wartislaw II Swantiboritz, who was Castellan of Szczecin, and thereafter the Rugian prince Jaromar I.

Despite his predecessors having joined the Holy Roman Empire in 1181, Casimir and Bogislaw II had to yield to Danish pressure put on Pomerania.

The Danish influenced Casimir's reign not only by appointing Jaromar, their vassal and ally, to be his legal guardian, but also by determining the northern borders of Pomerania-Demmin that were disputed by Pomerania and Rügen, with Rügen claiming the Peene river and Pomerania claiming the Ryck river further north to be the border.

The decision of Canut that had to be accepted by Anastasia favoured the Rugian demands, only the trans-Peene terrae Wolgast, Lassan and Ziethen were put under Pomeranian control with the larger part of the disputed area, including the terrae Lositz (Loitz) and Wostrose (Wusterhusen), remaining within Rügen.