cf. http://p-town.dmm.com/cb2/ (Japanese)
This "oshiri pen pen time",abbreviated as "OPT" is originally from the Pachinko game(machine) "cinderella blade"series.
According to what official site says,if you join this contest you post "Selfie-spanking pic" with "#自画撮りOPT"(lit.Selfie-spanking-time) and at the same time follow ＠DMM_pachitown on twitter.
And if your tweet attract best attention (e.g. most retweeted by others?)on twitter you win this contest.
Thanks to this event,we can see some Selfie-spanking pic on twitter.