Freelance and general work contracts in Japan typically fall into two categories. Each have their own requirements, but Keiraku by Sollective handles both equally well:
"Juninin" Contracts: A contract where work is compensated for by a time-basis (e.g. per hour)
"Ukeoi" Contracts: A contract which sets a fixed deliverable (e.g. a product or service) which is paid for by a fixed price