Tsumugu Kihara is one of the main characters in the series. He is a human with the roots in both the land and the sea. His grandfather (who he lives with and fishes with) was allegedly one of the sea-folk who came to live on land, which may be the reason why his eyes are such an unusual color.

    Since his early childhood, Tsumugu has been a calm, collected, and solitary person. Tsumugu is portrayed as being somewhere between merely stoic and matter-of-fact, rarely ever smiling or showing emotion at all. Tsumugu usually expresses no desire to act into anything, usually wearing a casual, bored look in his face. Tsumugu has a very inquiring mind when there is something he cares about, but at the same time, he had almost no tenacity of purpose, he prefers to observe then act. Despite his usually stoic demeanour, Tsumugu does have an emotional side, as he noted during his talk with Miuna, that he just doesn't know how to show it.

From Wikia

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