Beautifully wicked drama that depicted tragic things happened to tragic people.
Great acting from all casts. All in all, there’s no good and bad people in this story. People did what they did out of spite and to redeem themselves.

For those who didn’t understand last ending scene between Mayuko and Naomi, this review will be mainly wrapped around that particular scene.

The Ending Scene (Episode 4):
Naomi asked Mayuko to watch him swims to the buoy. As he walked to the shore, Naomi turned around for one last look at Mayuko whilst pointing his finger into the distance before swimming into the ocean.
He was mimicking the same scene performed by Tadzio in a 1971 film “Death in Venice” directed by Luchino Visconti.
The significance of this film’s ending scene and the director himself are important to Mayuko later on.

To summarise this film, Tadzio had a pursuer called Aschenbach who secretly followed him around Venice as his obsession with Tadzio’s beauty grew stronger. Towards the film’s ending, Aschenbach was stuck in the same situation as Mayuko, because both were unwell due to health conditions.
In this same scene, Tadzio turned around looking at Aschenbach and pointing into the distance (the same way as Naomi did to Mayuko). Aschenbach who was dying, yearned for Tadzio and still mesmerised by the boy’s beauty before passing away while trying to reach out to Tadzio.
[Updated in 2024: abovementioned cinematic parallels - https://easterndelights.tumblr.com/post/759516469940879360/kna-div ]

Based on both scenes, Tadzio was a symbol of youth, innocence and adolescence beauty to Aschenbach; in the same way that Naomi symbolised as a perfect ideal man to Mayuko.

In episode 1, Mayuko’s father praised Mayuko for having a keen eye for something beautiful when he saw the necklace that Mayuko found from the beach. As Yuki took that necklace from her, Mayuko took something beautiful from Yuki 30 years later.

When Naomi was born, Mayuko held baby Naomi and saw the beauty in him. She told Yuki that she might take him away, but Yuki never took that matters seriously.
Over the course of 20 years, Mayuko moulded Naomi’s personality and groomed him into becoming her ideal man. Naomi would have knew everything about Mayuko at this point - like he knew her favourite french poets are Verlaine and Baudelaire, and her obsession with the novel of “Chijin no Ai”.
After Naomi was freed from both of his parents, his wish to always be together with Mayuko came true - albeit it came with a hefty price.

Back in episode 1, Mayuko brought up a film called “The Leopard”, into a conversation with her mother where she reminisced the beautiful castle scene. That particular film was directed by Luchino Visconti.
Naomi might have also learned about Mayuko’s love for Visconti’s films, although the viewers never get to witness this scene.

Back to the ending scene, Naomi dressed Mayuko in all-white before heading to the beach. It was coincidentally the same as how Aschenbach wore all-white to see Tadzio for the last time.
When Naomi was pointing into the distance mimicking Tadzio's scene, Naomi wanted to show Mayuko that he was never the Naomi from “Chijin no Ai” and Mayuko was not his captor.
Instead, he is the Naomi that always yearned for Mayuko and her affection, despite all tragic things happened to Mayuko because of Yuki.

Mayuko was conflicted with her feelings at first, but did reciprocated and gave in to the decision to be with Naomi.
With Yuki completely gone from both of their lives, there will be no more malice and destruction as peace ensured.
Despite being bedridden and in a vegetative state, Mayuko regained her long forgotten youth and innocence by starting anew with Naomi.

When Naomi was tributing his Tadzio to Mayuko, it was a sign to trigger Mayuko’s memory telling her to yearn for him, as he will always be waiting for her return.
In the end, Mayuko understood what Naomi was signalling to her (hence she smiled).