Six siblings from the same birth, often looking very similar if not identical.
This also includes fraternal sextuplets (sextuplets of opposite genders, or sextuplets of the same sex but who aren't identical).
The most prominent example in Japanese media would have to be the Matsuno brothers of Osomatsu-kun. Another notable example are the Ooshima sisters from Heaven Burns Red. Though by being fraternal siblings, they're all of different heights, hair colors and breast sizes.
