Ether-Cosmos comprises of twenty pieces for piano. The length of each piece lasts about 1-3 minutes, except the piece no. 18 which is longer than 12 minutes. Ether-Cosmos No. 13 is about 2.10 minutes in length. This piece illustrates various techniques of motivic development such as rhythmic manipulation, augmentation, inversion, succession of the developed motives, and so on. No matter how the transformation does, it is still illustrating relationship with the original motive due to similarities of melodic contour and direction of movement, including intervals and harmonies both in vertical and horizontal context still involve with tritone. The pitch ranges are used independently both vertically and horizontally. The rhythmic patterns play an important role in motivic development which the structure of rhythmic motives is the one that can explain the unity of music. Therefore, to preserve the unity in Ether-Cosmos No. 13, the development of rhythmic motive plays an important role, especially in this free atonal piece.