The Utajima-maru returns a few days behind schedule, missing the Lantern festival. As soon as Shinji gets back he goes to Yashiro Shrine and gives thanks for his safe return, then heads to Jukichi's for a celebration. Two days later, out on the fishing boat as usual, Jukichi asks if Shinji heard anything from Uncle Teru. The boy replies in the negative and grows morose. However, he still feels self-sufficient after his adventure, and that evening when he sees the outline of a freighter sailing out to sea, he thinks about how he knows where that ship was going and what life is like on it because he has finally experienced the unknown.
Summer vacation is almost over but Chiyoko still has not returned to the island. After much pleading from her mother, Chiyoko finally explains in a letter how she had hurt Shinji and Hatsue and will not return until they are happy. She asked her mother to be a go-between and convince Terukichi to let the lovers marry. The lighthouse keeper's wife is distraught and fears her daughter might even commit suicide, as is sometimes the wont of emotional young girls. She decides to act as a go-between and resolve the situation.
She walks down the main street of the village in her best clothes and nears a group of the other village women, who have more free time since diving has not resumed after the festivities. They are energetically washing clothes and greet the lighthouse keeper's wife. She explains that she is going to stop by Terukichi Miyata's house for a moment, but realizes that this is strange to do without speaking with Shinji's mother about the proposed engagement. She asks Shinji's mother, unintentionally loud enough for the others to hear, if Shinji and Hatsue are doing well. Shinji's mother is hesitant, and the lighthouse keeper's wife asks if Shinji does like Hatsue. The mother assents, and bursts out that Uncle Teru is going to marry his daughter to Yasuo. The mistress of the lighthouse explains her mission and, after listening quietly, the mother replies, "I'll greatly appreciate anything you can do." Five other women who were listening decide to go as well, hoping a show of numbers will convince the old man.
The six women walk to the Miyata home and enter the empty room. No one appears to be home. They call their greetings, and Terukichi himself comes down the stairs. He agrees to hear what the mistress of the lighthouse has to say. The women join him in the sitting room, the mistress seating herself and the others standing nervously.
After a moment the mistress states that she is there because of Hatsue and Shinji. Terukichi turns to look at her and replies that if that is all she has to talk about, then they are done since he has already decided Shinji can be Hatsue's husband. He adds that they are too young at the moment and should be engaged for now, but when Shinji comes of age they will have a proper ceremony. He speaks further, explaining that he was angry at first when word of their love came out, but was disturbed by how affected his daughter was by their forced separation. He decided to set up a test and gave Shinji and Yasuo to the captain, telling him to report back on their behavior. The captain loved Shinji, and when Terukichi heard of the boy's courageous act, it was settled. There could not be a better husband for Hatsue. He concludes by reflecting, "the only thing that really counts in a man is his get-up-and-go. If he's got get-up-and-go he's a real man, and those are the kind of men we need here on Uta-jima. Family and money are secondary."
In chapter sixteen, Shinji can now visit Hatsue's home openly. One evening she meets him at her door; the two have a date to visit the shrine and then the lighthouse, announcing their engagement and expressing their thanks. They walk up the steps of the shrine slowly, savoring the pleasure of being together. Nature is also smiling down upon them – the night sky is filled with gleaming stars and the waves are peaceful. Shinji claps his hands in happiness and Hatsue prays quietly. Shinji is reminded of how all of his prayers came true, and is inexpressibly grateful. They offer the priest in the shrine office a red snapper, and he is pleased to realize he will be officiating their marriage someday.
The couple walk toward the lighthouse. Shinji suggests that he might take an exam to be a first mate; this could be done at twenty, and then they could marry. Hatsue smiles and says that would be wonderful. When they reach the lighthouse, the mistress opens the door and announces their presence to her husband, who invites them in. One stray remark about Chiyoko –- that she is returning tomorrow –- is unheeded by Shinji, who never had any idea of the anguish Chiyoko suffered because of him.
After supper, the lighthouse keeper gives a tour of the lighthouse to the young lovers. They look at the watch house first, Hatsue delighting in gazing out at the lights in the gulf and having Shinji identify them for her. They watch a large ocean liner come into view and then sail out across the Irako Channel and into the Pacific. They then go into the lighthouse itself, and view the small room at the top of the stairs where the lighthouse keeper performs his job. Tactfully, the lighthouse keeper leaves them alone.
Shinji and Hatsue stand together looking out the window, their warm cheeks nearly touching. Shinji is lost in thought, pondering how, despite all they had been through, they are now "free within the moral code to which they had been born, never once being estranged from the providence of the gods...that, in short, it was this little island, enfolded in darkness, that had protected their happiness and brought their love to this fulfillment..."
Hatsue laughs when she discovers the little pink shell in her sleeve and asks Shinji if he remembers it. He does, and he takes out his picture of her; he watches her caress it, knowing that she thinks it was her picture that kept him safe. In fact, "it had been his own strength that had tided him through that perilous night."
The Sound of Waves possesses a felicitous ending, one that, while not entirely unforeseen given the certainty of Nature's support of the lovers, is not completely assured. There does indeed seem to be an array of obstacles confronting the lovers. They can barely communicate, for one. Shinji knows they could not elope because he has no boat and no money. He also rules out the idea of double suicide, since it is not his nature to despair so completely and to act out in such a selfish fashion. Thus, it does seem like the only way in which the two of them can be together would be if Terukichi changes his mind, and the book repeatedly emphasizes his stubbornness; but this, amazingly, is exactly what he does.
When Chiyoko's mother, the lighthouse keeper's wife, nervously visits Terukichi to try and convince him that the two young people should marry (part of Chiyoko's redemption), she discovers to her delight and surprise that the old man has already relented of his own accord and now desires his daughter to marry Shinji. As he explains to the coterie of women, he was angry at first but then saw how adversely his daughter was affected. He gave Yasuo and Shinji the opportunity to work on the ship and listened to the captain's reports of their behavior. He greatly admires Shinji's pluck and endurance during the storm, and "decided I'd never be able to find a better husband for Hatsue" (175).
Terukichi continues with an assertion of why precisely Shinji now appealed to him so much: "The only thing that really counts in a man is his get-up-and-go. If he's got get-up-and-go he's a real man, and those are the kind of men we need here on Uta-jima. Family and money are secondary. Don't you think so, Mistress Lighthouse-Keeper? And that's what he's got –Shinji –get-up-and-go" (175). These wise words reveal Terukichi's rationality and ability to remedy his past mistakes and errors of judgment. He is no longer inclined to consider Shinji's poverty as an impediment to a marriage to his daughter, for Shinji's good, strong, and moral character has been established. Also, Terukichi's comment that Uta-jima needs men like Shinji is not surprising in light of Mishima's description of the old man as the personification of the island itself. It is appropriate that he would keep the fortune of the island in mind when making a judgment on Shinji's value.
Shinji's coming-of-age is even more pronounced upon the return to the island. While he throws himself into the old and familiar work, particularly to conceal his melancholy upon not hearing anything from Terukichi, he still possesses a "strange feeling of self-sufficiency" (167) that does not leave him. When he sees a white freighter out upon the sea, he no longer finds it alien and unknown; rather, "Shinji felt a new emotion. 'I know where that ship is bound for...I know what sort of life they live aboard it, what sort of hardships they have. I know everything about that ship'" (167).
He remembers the sensation of holding fast to the rope and how he finally had "actually touched that 'unknown' at which he had previously stared from a great distance" (168). Shinji has been irrevocably changed. Whether or not he still grows up to own a fishing boat with his brother and stays near the familiar shores of Uta-jima, he is forever changed by the widening of his ken. Unlike his brother Hiroshi, Shinji has internalized the sights, sounds, and sensations of the outside world and will never be the same. This is truly emphasized by the novel’s ending, when Hatsue thinks it was her love that saved Shinji, but he knows it was his own strength. The success of the love story in the novel relies on Shinji’s maturation and strength, while similarly, it was, of course, the taste of first love that led him down this path; therefore, the love story and the coming-of-age story are inextricably intertwined in The Sound of Waves.