The rabbit tattoo on their hands signify their association with the underground tournament 'The Rabbithole'. Participants are known as Rabbits and the only way for them to recognize a genuine Rabbit is to do the rabbit hand signal as a greeting and expect a greeting of the same manner. The tattoo shows they are top rabbits and are bold enough to show the world their affiliation with Rabbithole, their rebellion against authority and their violent lifestyle.

The one wearing the hat is known in Rabbithole as 'Mad Hatter' due to killer techniques applied in fights. The blue-haired guy is known as 'Mercy' due to his tendency to kill his opponents when they are suffering too much pain.

lol I got lazy towards the ending so Mercy got squished in a tiny box.