純潔 is associated with “chastity” but with the direct meaning of clean, innocent, and pure.

If you were expressing the idea of a “pure heart” in Chinese, while not literal, this would be the word you would use.

In Japanese, this word is sometimes used to express purity.

In Korean, it describes purity, chastity, virginity, and innocence (basically the same as the Chinese definition).

青梅竹馬 means “green plums and hobby-horse.”

Figuratively, it means “innocent children's games,” “childhood sweethearts,” or “a couple who grew up as childhood friends.”

This phrase may sound a little strange as it's a kind of Chinese proverb or idiom. It makes much more sense in Chinese than in English.

純情 means “Pure Heart” in Chinese, Japanese Kanji, and old Korean Hanja.

It's used to reflect the ideas of being “pure and innocent.”

Depending on the context in which this title is used, it can relay “self-sacrificing devotion” or, in some cases, “naïveté.”
This would be in the same way we might refer to a young girl giving her lunch money to a beggar on the street. She has a pure and precious heart but perhaps is also a bit naive.