The creator of Blue Lock: Rivals thought kids on Roblox might like a soccer video game with an anime vibe. It sold a few months later for more than $3 million.The 19-year-old, who asked that his name be withheld because he has never shared it publicly, made the game in just three months with the help of co-developers. It attracted more than 1 million simultaneous players following its release last year, he said, generating $5 million a month in purchases for Roblox Corp., the popular gaming plat...