This is an extra chapter of Iwaihime, written after the main story by Ryukishi07 and originally included in the Japanese "Matsuri" re-release for PS4 and Vita.

Story

Mayu Hinagata is the LCSC's dear advisor, a veritable fountain of inspiration and wisdom.
But being so kind can be draining.
An innocent surprise party brings painful scars back to the surface to haunt her.
And dark, ancient teachings revive nightmarish memories that threaten to clog fate's machinery with soot...

Finally focus on Mayu Hinagata→Learn more about your dear, gorgeous teacher→Uncover new secrets and old wounds→Drive a grateful nail into evil's black coffin!