Hello Miles

If you have overstayed your visa, you are now in an irregular situation and there is no chance to revert that unless you go back to Asia and get a new visa to come back to Spain.

If you stay in Spain , taking the risk it involves, you will be able to apply for Residency By Settlement after 3 years continuous stay and providing you have a work offer. You can read more about this type of application here.

Regards