na-adjective, noun
sensitive; impressionable; emotional
Describes a person who is easily affected by external stimuli or emotions; often used for adolescents or sensitive personalities.
彼は多感な少年で、小さなことにもすぐ感動する。
He is a sensitive boy who is easily moved by small things.
多感な時期に読んだ本は一生忘れない
Books read during one's impressionable years are never forgotten.
Composed of 多 (many) and 感 (feeling, sensation), literally 'many feelings'. The exact historical derivation is uncertain, but the kanji combination naturally conveys the idea of being easily affected by various emotions.