The production team behind the live-action drama Shiawase ni Naritai Masamune-kun (幸せになりたいマサムネ君) has revealed additional cast members for the series. Based on the manga by Yonemai, the story follows Masamune — a man who, despite having a girlfriend he loves, ends up creating a secret relationship on the side, entangling himself in a complicated web of romance.
New Cast Additions
Akita Shiori joins as Hayakawa Momoka, Masamune’s 26-year-old office-worker girlfriend of ten years. Meanwhile, Saito Nagisa plays Marumaru-ko (〇〇子), a 22-year-old office worker Masamune meets at a shared-seating izakaya after convincing himself that Momoka has grown tired of him. After spending a night together, she finds herself completely falling for him.
Also announced are Kan Hideyoshi as Tsubasa, an elite salaryman who has been friends with both Masamune and Momoka since their university days, and Maehara Ko as Nakata, the editor-in-chief at the publishing company where Masamune works part-time.
Cast Comments
Akita Shiori (as Hayakawa Momoka)
Even after ten years together, the things you most want to say are the hardest to express. The frustration and miscommunication in this story feel very real. I want to carefully portray the special closeness between the two of them, as well as Momoka’s charm and humanity. Reading the script and the original manga, I was completely drawn in by Masamune’s hopeless flaws and the unpredictable plot — I finished it in one sitting. I think different viewers will feel different things watching this, and I’m really looking forward to the broadcast.
Saito Nagisa (as Marumaru-ko)
I was so happy when I received the offer. After reading the original work, I felt it was a warm story that depicts each character’s feelings and inner conflicts in a charming and thoughtful way. Marumaru-ko plays a key role in the narrative, and I think many viewers will find her relatable. I’m approaching filming with the goal of fully conveying her appeal. It’s a series that will make you laugh, feel wistful, and experience all kinds of emotions — please look forward to it.
Kan Hideyoshi (as Tsubasa)
I was truly delighted to be offered a role in this project. The story’s tightly interwoven relationships and the shifting distances between characters are portrayed with striking realism. I deeply resonated with the question of “who are you expressing yourself for?” I’ll approach every emotion Tsubasa feels with sincerity and care.
Maehara Ko (as Nakata)
Look up the word “happiness” and you get definitions like “a state of contentment” or “a situation with no dissatisfaction.” Is there really anyone in this world with absolutely zero complaints? Masamune is chasing something incredibly difficult. Early in filming, he doesn’t look happy at all — and honestly, that’s reassuring. I’m looking forward to seeing where the story goes from here.
Broadcast & Staff
The drama premieres late night on Tuesday, July 7, 2026, airing on MBS, TBS, CBC, HBC, and RKB. Yamaura Miharu directs, with Takeda Yuki handling the screenplay. The original manga is published by Bungeishunju.
Full Cast
- Nakazawa Motoki — Masamune
- Akita Shiori — Hayakawa Momoka
- Saito Nagisa — Marumaru-ko (〇〇子)
- Kan Hideyoshi — Tsubasa
- Maehara Ko — Nakata
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