Reimu and Marisa's combination attack:
連符「陰陽スターマイン」 Combination Sign "Yin-Yang Starmine"
The attack damages all enemies, and may cause the "tinnitus" status.
EDIT:
"Star mine/star mine" is a type of fireworks. In Touhou, it is used in Udonge's SWR
spell card, Illusion Bomb "Myopic Fireworks (Mind Starmine)".
Probably due to Japan's love of fireworks, "starmine" is a somewhat popular word there, e.g. there are pop songs titled "Starmine", so it's not like this is a super obscure word that only ZUN would use. I also couldn't find any proof about him being involved with the game. These, among other things, seem to indicate this spell card is non-canonical.
BTW, this reminds me of the one very special semi-canonical spell card, ZUN's
contribution to the doujin artbook "Touhou Last Word Collection": 夢符「幻想一重」 Dream Sign "Gensou Hitoe".
Gensou = "fantasy". There is a phrase in Japanese, 紙一重
kami-hitoe "(separated by) a sheet of paper", i.e. a tiny difference, a fine line. So the name of the spell card can be understood as, "what separates fantasy and reality is as thin as a sheet of paper".