"Lazy" is what I did when I discovered a total absence of Sekai headbadge decals on the interwebs: I went to cafepress and got a vinyl "rising sun" decal instead. Looks pretty sharp on that navy blue bike, and easily removable should the time come:
Nothing a purist would consider, sure, but with my fenders and a copilot baby seat strapped to the rear end, purity is pretty much shot to heck anyway!