An antidote was unlikely to exist to the poison that had been used on Rex and even Milo himself was unlikely to be able to have a way to cure and get rid of such poison, but Adam had someone in mind and that could fix Rex's condition.
With Milo dead, Adam was relieved and as soon as he relaxed slightly, he was overcome with the pain and strain that his body was suppressing due to the situation he was in.
"Marco guard me until I recover," instructed Adam, before activating the Ethereal Recovery Skill.
Although it was extremely unlikely that Adam would be attacked in the middle of nowhere, it was better to be safe than sorry, while he also didn't need that long to recover.
Marco did as Adam said and walked over to his side and stood there on high alert for an entire hour, before Adam told him that he should start recovering as well.