My surname I "translated". For my given name, I originally chose a simple Chinese name based on sound similarity (e.g. "Da" becomes 大 [da4] "big; great"). All it takes to make this a Japanese name is to settle on a reading for the characters. So far, I've been using the kan-on "Daimon" because it's close to the Korean (Daemun) and Cantonese (Daaiman) pronunciations. You could equally well read it "Obumi", but I've never liked the sound of that.