These mascots are known in Japan as kawaii(for more info on kawaii go check out Matt's book-"Hello, Please"), and in this case are specifically geared at celebrating or publicizing a major event. The SEVEN kawaii are best summarized by Matt himself:
Clockwise from left, you've got Oniide (a super-cute crown-of-thorns starfish, nicknamed the "demon-star" in Japanese for its toxic spines), Shota (the boy with coral for hair), Kacchi, Chu, and Zou (a trio of coral polyps), Taiyo-Kun (the sun), Unibo (a sea urchin), Kanirin (a crab-girl) and Jangurasu (sea grass). The mascots were named in a nationwide competition; a 76-year-old from Fukushima submitted "Shota," while a 7-year-old from Tokyo came up with "Taiyo-Kun," showing the huge popularity of "working characters" (as we call them in Hello, Please) across a wide demographic in Japan.TWO of these mascots are prominent coral-reef echinoderms. Both of which were taxa included in my recent post on corallivorous echinoderms...specifically Acanthaster planci, the Crown-of Thorns Starfish
Oniide is the very cute cartoon version not to be mistaken for this formidible beast:
and Diadema, the black needle urchin (this is my interpretation-there are quite a few coral reef echinoids that this might represent) as represented by Unibo (think of Uni from your local sushi restaurant)
Regardless of their perceived "threat" or "menace" both of these organisms occupy positions of ecological importance in coral reef systems and so, widespread awareness of not just the reef but its component inhabitant animals remains an important priority.
And hence... cool Japanese mascots!!