true friend
A friend who is genuine, loyal, and trustworthy, often contrasted with superficial acquaintances.
困ったときに助けてくれるのが真の友だ。
A true friend is someone who helps you when you're in trouble.
彼は私にとって真の友と言える存在です。
He is someone I can call a true friend.
Compound of 真 (しん, 'true') + の (possessive particle) + 友 (とも, 'friend'). The phrase is straightforward and transparent.