Shin Adachi doesn’t go in for conventionally likeable characters. In his breakout film as a screenwriter, “100 Yen Love” (2014), a 30-something woman decides to become a boxer for the sake of a guy who, unequivocally, is a total jerk.

Adachi’s directorial debut, “14 That Night” (2016), revolves around the exploits of a junior high-school student hoping to fondle a porn star’s breasts.

“I think I’m showing the kinds of foibles that most normal people have,” he says with a shrug. “When you just show people as they are, those kinds of elements are going to come out.”

In his sophomore feature, “A Beloved Wife,” which screens in the main competition at this year’s Tokyo International Film Festival (TIFF), Adachi casts Gaku Hamada as Gota, a fictionalized version of himself who is unlikely to win many popularity contests. An unsuccessful screenwriter, Gota spends most of his time lamenting the fact that his long-suffering spouse, Chika (Asami Mizukawa), doesn’t want to sleep with him anymore.

The film follows the couple and their young daughter as they head to Kagawa Prefecture in Shikoku on a fact-finding mission for one of Gota’s scripts. Chika’s talent for berating her husband is matched only by her determination to save money wherever possible, even trying to break into the hotel where they’re staying in order to conceal the fact she’s booked a single room for a family of three.

Then again, Gota seems to deserve much of the abuse: When he isn’t making pathetic attempts to initiate sex with his wife, he’s sending flirty messages to an old flame, watching porn on a virtual reality headset and getting hauled in by the police for trying to peep up the skirt of a woman he finds passed out in the street.

Just how autobiographical is all of this?

“Well, it’s based on my actual experiences,” Adachi says. “He’s very close to the real me, but the film makes it all look better.”

He admits that casting Hamada — whose diminutive stature and childlike face makes him almost impossible to dislike — was a way of making the character elicit more sympathy from the viewer. When I tell him that I still find some of Gota’s behavior unforgivable, he seems taken aback — as I suppose you would be if someone told you that your alter ego was a scumbag.

“Gota probably seems like a more ordinary, respectable person to others,” he says. “But he and his wife have spent a long time together as a couple, and when you do that, all your ugly qualities are gradually revealed. That’s why you have more arguments and conflict. When you’re married, it brings all of that into the open.”

Chika’s frustrations boil over during a hysterical confrontation with Gota at the film’s climax that teeters between comedy and melodrama, and is likely to divide audience opinion.

“That’s the one scene we didn’t rehearse in advance,” says Adachi. “I was worried that if we did that, the performances would lose spontaneity, and they’d just end up doing it like they’d done it in rehearsal. I thought it turned out well, so we only filmed one take.”

The film’s humor is rooted in a very unvarnished depiction of domestic life. Adachi says he invited Hamada and Mizukawa to his home for the first read-through of the script “so I could give them an idea of the kind of place I live in” (rather less fancy than their own abodes, one presumes).

Many of the scenes in the movie take place in cramped apartments and hotels, where the family — quite literally — let it all hang out.

“Films and TV shows wouldn’t normally show a father standing naked in front of his daughter, or taking a leak with the door open,” says Adachi, “but I included those moments because I wanted to show people living a regular life.”

This emphasis on normality is a recurring theme during our conversation, and it stems from one of his original inspirations. Growing up in 1980s Japan, Adachi was enthralled by the TV dramas of Taichi Yamada, a celebrated screenwriter known for series such as “The Roads Men Travel” (1976-82) and “Assorted Apples” (1983-97).

“I loved the way there weren’t any cool characters or heroes in his shows: Whatever I watched, they were always just regular people” he says. Only when he started writing his own scripts did he discover the secret of Yamada’s approach.

“It’s about how severely he looks at ordinary people,” he says. “His dramas don’t give you a cheap pick-me-up: They’re really unsparing, but they leave you with a sense that this is why we need to do better as people. It’s harsh, but it’s also really big-hearted, and I like that.”

Like his counterpart in “A Beloved Wife,” Adachi has gone through a few rough patches during his career. After studying under the late Shinji Somai and briefly working as an assistant director, he made his screenwriting debut with the little-seen wrestling comedy “Mask de 41” in 2004 and spent the following decade struggling to make his mark.

While his script for the LGBT drama “Schoolgirl Complex” (2013) caused a minor stir, it was the following year’s “100 Yen Love,” directed by Masaharu Take, that turned him from a nobody into one of Japan’s hottest writers. The film premiered at TIFF and went on to win Japan Academy Awards for Adachi and its star, Sakura Ando.

Although he’s worked on adaptations, including last year’s delightful “Shino Can’t Say Her Name,” Adachi is notable for the number of original scripts he’s penned. The dearth of such screenplays in mainstream Japanese cinema is a regular talking point among critics, but does he see this as a problem?

“A lot of my scripts are originals, but that’s because I’m only doing low-budget films,” he says. “Those kinds of films tend to be based on original screenplays, because you’re not going to attract successful properties in the first place — so I don’t think there’s a shortage as such.”

Adachi adds that he does not find it necessarily better to work from an original script.

“Adaptations are fine as long as they make for a good film,” he says, “but when a project just gets off the ground because of how many hundreds of thousands of tickets they think they can sell, that’s when you run into problems.”

Has he been offered any projects like that?

“No, but I’d like to be,” he says. “I think I could try some interesting things.”

As with “14 That Night,” “A Beloved Wife” started life as a novel, which Adachi published in 2016 under the title “Chibusa ni Ka” (“Mosquito on the Breast”). Giving your own book the movie treatment is perhaps more common in Japan than in the West; directors Mika Nishikawa and Momoko Ando have also brought their own novels to the screen in recent years. Adachi says it’s a good way of ensuring your original vision survives intact, but there’s an inevitable downside, too.

“When you take something all the way from novel to film, that’s a really long relationship,” he says. “It’s not exactly like being married, but you still gradually get fed up.”

“A Beloved Wife” will be screened at Toho Cinemas Roppongi Hills on Nov. 1 in the main competition of the Tokyo International Film Festival. For more information, visit 2019.tiff-jp.net/en.

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