understanding person; supporter
Refers to someone who understands and supports another person, their situation, or their views. Often used for a sympathetic ally or advocate.
He is one of my few understanding supporters.
There are few people who understand and support the new policy.
味方 is an 'ally' or 'person on one's side', often in a conflict or competition; 理解者 is about emotional or intellectual understanding.
Compound of 理解 (understanding) and 者 (person).