OSAKA — Seiho Hayakawa started making music the way a lot of curious kids growing up in the digital age did — by fiddling with his cell-phone ringer. But he eventually plunged headfirst into the world of jazz as a high school student, with a trumpet at his side. Those early experiences stuck with Hayakawa, 24, who now records under his given name. He produces electronic music of many moods, from thumping hip-hop-inspired fare to jazz-tinged chill-outs.