志半(こころざしなか)ばで倒(たお)れ、さぞ無念(むねん)だったことだろう。

Having fallen before achieving his goal, he must have been deeply frustrated.

彼(かれ)は敗北(はいぼく)の無念(むねん)を晴(は)らすべく、鍛錬(たんれん)を重(かさ)ねた。

He underwent rigorous training to overcome the mortification of his defeat.

無念(むねん)の思(おも)いを