PC - player character
The Hippocratic Oath, as many know, is an ethical oath that many in the medical profession are required to take in order to begin practice. However, in its earliest forms, it was an oath to Apollo, Asclepius, Hygieia, and I think another Greek deity. The point is, it was an ethical oath taken by practitioners of medicine to various Greek gods, promising to uphold certain ethical standards. However, one clause in the earliest known copy says that those who take the oath cannot do harm or injustice to a patient.
If the PC had some kind of background in medicine, even as small as having been a temporary med student, they may have taken this oath. Likely as a joke in an undergrad class, but nevertheless, an oath is an oath. Assuming they have, let’s look at one of the first things the PC does; get the wine for Asterion and help him heal.
By doing this, the PC would technically have taken Asterion as a patient, even if it was only temporarily.
Now, looking at it all as a whole; the PC has taken an oath to Apollo to not harm a patient and has technically taken Asterion as a patient. Meaning the PC cannot harm Asterion and literally no one can try to make him.
*waits for Agros’ head to explode*