A couple of stories that illuminate this sometimes confounding activity. In Hawaii, the deck sums it up:

Passive fun isn’t for hard-core anime fans who toil to dress the part

and the story digs in:

About an hour and a half later, Sasaki says in her gentle voice, “So, anyone want to start on buckles?” The eight group members clear away dinner, head for the soda boxes and bring out … costume pieces. Half contain Styrofoam pieces that will become shoulder pads. The other half are full of vinyl pieces cut into arrow shapes that will become buckles for jackets — the main reason for tonight’s get-together.

MEANWHILE, Japan Times focuses on some new establishments in the Shibuya os Tokyo where you can pretend you’re in prison, complete with giant needles. Whee!

Each version of Alcatraz incorporated some variation on the basic theme, and the Shibuya E.R. seems to strike the right balance with its unique blend of (im)pure cosplay. In short, it is both a maximum-security prison and an emergency medical room where it’s Halloween every night and ghoulish jailers and macabre medics take charge. Talk about a spanking.

Fortunately, it is all just play. As soon as you step out of the elevator onto the second floor, you are in a holding cell. The doors are controlled from the inside, so you must wait until they are ready to admit you. Once inside, your induction will be “processed” by the resident on duty. The night nurse will be summoned to assist. It is her job to see that any potentially dangerous inmate in each fresh intake is securely handcuffed. Remember: good behavior will be rewarded, so be on your best or it might be you — or at your worst if you want it to be you.

After that, disinfection procedures begin. There are simply no words to describe the size of that needle, except for maybe “ouch!” Well, not really. It is big, but I don’t want to spoil the gag by revealing exactly what they do with it. You’ll have to go and find out for yourself.