Likely related to Erica or Ericka, from a Germanic root meaning eternal ruler or ever powerful.
Erka is likely related to Erica or Ericka, and those forms ultimately connect to Germanic roots meaning eternal ruler or ever powerful. That etymology gives the name a strong, compact sense of authority beneath its softer spelling.
The shorter form Erka feels direct and lightly modernized. It has a briskness that makes it sound less formal than Erica, while still retaining the same serious root meaning. In use, it can seem both delicate and forceful, which is a useful tension in a small name.