恩, 恩人 and 恩返し: kindness, a benefactor and repayment
Distinguish received kindness, a benefactor and the wish to return kindness. Read the desire to help the next generation separately from completed repayment, and keep the crane's return of a favor within the folktale.
恩 names the kindness received
「困ったときに助けてくれた先生の恩を忘れない。」 (I will never forget the kindness of the teacher who helped me when I was in trouble.)
Another example expresses wanting to repay received kindness by helping the next generation. Receiving kindness and wanting to return it are different parts of the relationship; the wish does not report completed repayment.
恩人 is the person who helped
「命を助けてくれた医師を恩人と慕っている。」 (I regard the doctor who saved my life as my benefactor.)
A further example reports expressing gratitude in a letter to a benefactor from the speaker's younger years. The benefactor gave help, while the speaker received it.
A wish to repay and a folktale about returning a favor
「育ててくれた祖父母に恩返しをしたい。」 (I want to repay my grandparents for raising me.)
Another example reports reading a folktale about a crane returning a favor after being helped. Keep the wish concerning the grandparents and the folktale's events separate from an actual completed repayment by the speaker.
Does 祖父母に恩返しをしたい say the speaker has already repaid the grandparents?
Show the answer and why
No. It expresses wanting to repay the grandparents for raising the speaker. 恩 names received kindness, 恩人 the person who helped, and 恩返し returning kindness; this sentence states a wish rather than its completion.