Small Freelance Jobs on Humanities Visa – Tax?

If I have a humanities visa on a full time contract, and I want to do a few random freelance jobs to supplement my income, how do I go about correctly filing tax?

  • my main company does my tax filing for this job
  • gigs would be within the visa category
  • my contract does not prohibit additional work
  • they wouldn't be more than 30,000 JPY each

by wasabonbon