誠心誠意 (せいしんせいい) — in all sincerity; with one's whole heart; whole-hearted devotion
誠心誠意
せ い し ん せ い い
In all sincerity; with one's whole heart; whole-hearted devotion
彼
は
誠心誠意
、
彼女
に
尽
くした
。
He devoted himself whole-heartedly to her.
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