The kokuji 粂 【くめ】 exists, defined only as a name. The character is clearly an amalgam of 久 and 米 used in a man'yogana-like manner, but:
- Why did this particular surname get a designated character?
- Does the surname have a meaning, or is it opaque?
My suspicion is that there was a well-known 粂 who chose to write their surname in an idiosyncratic way, which others sharing the name came to use. If so, who was this individual?
The creation of ideograms is presently extremely rare for reasons related to standardisation and data entry, but the period when kokuji were being created suggests this was not always the case.