1Cover rakkyo with water in a non reactive vessel and add salt. Give it a good shake and leave at room temperature for 3 days.
2Drain shallots and in the same vessel add sugar, vinegar then rakkyo and refrigerate for around 3 weeks.
I find for these ratios of salt/sugar and time, three weeks is a desirable period in which to let them bathe, you might prefer a week or 2, perhaps even longer...
They will last longer in the fridge than is necessary as salivation at the mere sight will propel rapid stock reduction!