Onee-Sama; meaning big sister or older sister in japanese.
"-Sama" a japanese honorific that signifies high ranking or respect for someone.
This trope refers to a motherly or mature girl who is caring, kind, generally very sweet, and is seen as a cool by the ones she mothers.
Some great examples for the Onee-Sama trope would be Tohru Honda and Kisa Sohma from Fruits Basket, Tami Nishimikado and Naru Sekiya, and the song Doki Doki Yuri Gakuen sung by Hatsune Miku and Rin Kagamine. (See song above.)
Also see; Oneeshota, Oniiloli
Or Senpai and Kouhai.
