What’s a member of a group that just DEFINES the group?

Like if that member wasn’t in the group, the entire group’s concept would just fall apart. For example, I would say Wonyoung from IVE. Her entire aura and looks is basically the embodiment of IVE as a whole. Also would argue Yunjin in Le Sserafim with her confident personality or Hyein in Nwjns for her light, youthful presence that the group represents