What is the meaning of “The Sailor who Fell from Grace with the Sea”? How does Noboru define his own “hero” or “belief”

The title of the novel by Yukio Mishima, The Sailor who Fell from Grace with the Sea, refers to one of the main characters, Ryuji, who is a sailor. The other main character of the book—a young boy named Noboru—looks up to Ryuji because he believes him brave to depart from loved ones on land to conquer the sea. When Ryuji retires his mariner career and starts dating Noboru's mother, this disappoints Noboru greatly. Ryuji falls from Noboru's grace, and the latter sees the former as a weakling and, therefore, an enemy.
Noboru has a skewed idea of what manhood is. He believes men who sail and follow their own path, away from the society found on land, were akin to gods. This way of thinking and viewing the world reflects the author's own hyper-masculine attitude and reputation in Japan before his death. Noboru not only has a caricature vision of manhood, but he also follows a strange self-concocted belief system. This illustrates Noboru's psychopathic tendencies and delusional way of thinking.
https://www.japantimes.co.jp/culture/2015/07/25/books/book-reviews/sailor-fell-grace-sea-shows-yukio-mishima-invoking-primitive-male-fears/