Even though Oceanid got a modified divine body and regained a fragment of his divine power, most of his divinity was still stripped off. He had to start anew like the other Gods helped by Elysium Goddesses.
After Oceanid stated his oath to purify the soil and water of corruption, Rhea cast an additional restriction on Oceanid's soul and body to prevent accidents.
"Do you need to go that far?" Aether raised his eyebrows. Oceanid already stated the oath with Heaven as a witness and one's divine soul as the price, similar to Timus. However, Rhea still put a slave mark on Oceanid.
"It will disappear once he completes his task. Unlike the God of Trade's upgraded immunity, he must absorb the corrupted energy during the purification. This mark will work to protect him from contamination." Rhea explained a little to avoid misunderstandings.
Accept responsibility for your actions, be accountable for your results, and take ownership of your mistakes