"[Touhou Voice Drama] the reimu's happy holidays", or Kusso☆S2, is a voice drama produced and uploaded by Atouda Ako on Dec 2nd 2014.
Atouda himself named it "Firefly☆" (ホタル☆). Since it's the sequel to Kusso☆ (Kusso S1), it got named Kusso☆☆. It's the last entry in the Kusso series that is Natural Cookie☆(i.e. not deliberately made to be Cookie☆ material). Despite the name, the voice drama is more focused on anal than scat.
Details around the work were provided in the voice actor qualifying phase but not the risks associated with Cookie.
Summary of the plot
Reimu visited the Hourai Proctology department. Upon telling Eirin that she noticed blood in her excretions, Eirin diagonsed her with ripped hemorrhoids and began a palpation. At first, Eirin inserted one finger into Reimu's butt, then came a pen light to confirm the pain. As Reimu assured she was fine, suddenly, she got fisted. Then Eirin's head was inserted into the anus and, finally, her entire body. Then, the assistant also enters Reimu's rectum. After she was asked "Won't you come in, too?", Reimu entered her own rear end. Inside, she met Eirin and Udonge in firefly suits. Thereupon, Reimu began manically screaming "I caught the firefly" and laughing. With the final line from Eirin "Come here, firefly", the curtain closed.
It might be overshadowed by Kusso☆S1 and Kusso☆S3 but, due to the performances of Shinonome and Akira, it keeps itself afloat together with Kusso S1. It resurged interest after Koga played in other voice dramas, and from March 2017 until June 2018.