Her family name "Tsukumo" comes from "tsukumogami", her species of youkai. The motif of hers might be derived from "Bokuboku Biwa" (琵琶牧々), a tsukumogami transforming into biwa houshi.
Benben and Yatsuhashi shares the same ability (making music of their own), like Cirno and Letty Whiterock who shares one ability (Ability to Manipulate cold/chill, even their level is different.)
However, unlike the others, Benben and Yatsuhashi don't have blood relation, they are sister because two Tsukumogami are born at the same time from musical instruments.
Benben and her sister are currently the only characters who both appear as midbosses at the same time.
According to ZUN, Benben makes no sound when she chews, and she can even play the biwa using her teeth.
Benben and Yatsuhashi share the same theme called Illusionary Joururi. Mima and Sariel, and the Prismriver Sisters share different themes as well.