The three black Ryus represent the Ouendan, a trio of stern muscular characters wearing black uniforms led by their headband-wearing leader.
The stage represents Tsuyoshi Hanada's house, the first stage of the Ouendan's debut game, Osu! Tatakae! Ouendan.
The music track represents the musical theme of Steel Diver, which was released on the Nintendo 3DS along with Osu! Tatakae! Ouendan.
Ryu's favored Focus Attack and the Attack Power ↑ rule reference the plot of the Osu! Tatakae! Ouendan series where the Ouendan cheers for people in need.
Other trivia:
This spirit's Support type and Critical-Health Stats ↑ ability further references the Ouendan's role in the Osu! Tatakae! Ouendan series by cheering for people in need, which is shared with the Elite Beat Agents spirit, an international variant of Ouendan.
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