According to Yomiuri Online, two men have been arrested for performing "improper acts" in hotel rooms with the same 12 year-old girl on multiple occasions earlier this year. The girl met both men—one is a 49 year-old Yokohama resident and the other is a 36 year-old Chiba resident—through her 3DS. Yomiuri Online doesn't specifically mention SwapNote and says that the girl used the 3DS's online function to access an online dating site. A Mainichi News report, however, specifically does.
Mainichi reports that charges for child pornography have also been filed against another man, aged 44, who had allegedly two girls—then aged 11 to 12—send nude photos through SwapNote, or "Itsu no Ma ni Koukan Nikki" (いつの間に交換日記) as it's called in Japan. This man, a resident of Aichi Prefecture, has confessed to the acts.