Daniel Nico Laudit says he does not cry easily. He decided to test his mettle this month in a movie theater in Manila, and documented the experience for his 4.5 million followers on TikTok.

Before the screening, he filmed himself dancing and beaming and said to the camera: “Me before watching ‘How to Make Millions Before Grandma Dies.’” About two hours later, he uploaded a very different version of himself: wiping away the tears from his eyes in a bathroom.

“I went straight to the restroom after the movie because I wanted to cry out loud,” Mr. Laudit, 24, a content creator, said in a telephone interview. He said he cried some more when he got back home.

Reactions like Mr. Laudit’s have made the movie, which was filmed in Bangkok mostly in the Thai language, a runaway hit across Southeast Asia. In the Philippines, tickets were sold out on its opening day, theaters had to add more screenings to meet demand, and one chain started handing out tissues to viewers. In Singapore, it topped the box office from June 6-9. In Indonesia, it has drawn millions of viewers. In Thailand, it is the highest-grossing title of the year so far.

The plot revolves around an aimless and unemployed young man, M, whose sole ambition is to livestream his online games. He volunteers to take care of his maternal grandmother after he finds out she has Stage 4 cancer. His motivation is not filial piety; instead, he hopes that he can inherit her house.

After M moves in with his grandmother, he develops a closer understanding of the complicated characters that make up his Thai-Chinese family: Chew, his long-suffering mother who feels that only she can step up to take care of her mother; Soei, the good-for-nothing youngest uncle who borrows and steals from the grandmother; and Kiang, the eldest uncle who is preoccupied with his daughter and materialistic wife.

“It talks about the thing that we all have in common, which is family,” said Pat Boonnitipat, the director of the film.

This part of the world is “familiar with many generations living in the same house. I think that kind of upbringing creates a unique feeling in your memory,” said Mr. Pat, 33.

The movie explores the tensions that arise in a family before the impending death of one head of the household, and the gender biases that persist. In one memorable line, Chew says, “Sons inherit the house, daughters inherit cancer.”

The grandmother, or “Ah Ma,” played by the first-time actress Usha Seamkhum, is brusque and bristly, although viewers soon get to see that underneath that tough exterior, she loves her family members deeply, and that she is lonely. Many viewers said they loved the chemistry between Ms. Usha and her co-star Putthipong Assaratanakul, who plays the grandson.

Mr. Putthipong, known more popularly by his nickname, Billkin, is famous in Thailand as a television actor and pop star.

“The strength of this movie lies in the storytelling and how it draws the audience into the story, allowing them to compare the story in the film with their own personal lives,” said Angeline Kartika, 24, a content creator in Jakarta, the capital of Indonesia. She saw the movie last month.

Like many viewers, Joy Ni Ni Win, a digital marketing executive in Mandalay, Myanmar’s second-biggest city, said she heard about the movie on TikTok.

“It roused my interest to see — ‘OK, why are people crying so hard?’” said Ms. Joy, 28.

She quickly understood. Right after the movie’s closing credits, a friend filmed her in the theater with tears streaming down her cheeks.

Diana Setiawati, who watched the movie in Yogyakarta, Indonesia, said it made her think about how she spends too little time with her mother. After the movie was over, she immediately called her.

“How to Make Millions Before Grandma Dies” is the first feature film for Mr. Pat, a self-taught filmmaker who previously worked in television. It is an unusual hit in Thailand, he said, where horror and comedy movies typically rule the box office. The film will be screened at the New York Asian Film Festival in July.

The movie is based on a script by Thodsapon Thiptinnakorn, an established scriptwriter. Mr. Pat expanded it, drawing on his own experiences. His maternal grandmother, now 92, was diagnosed with Stage 4 breast cancer 20 years ago. She helped raise him, and the two still live together. He also added more characters, which he based on his Cantonese mother’s family, describing the representation as “exactly the same, even the dialogue.”

They resonated with viewers like Shirley Low, who is the chief marketing officer of Golden Screen Cinemas in Kuala Lumpur, the capital of Malaysia.

“Everything there was like: ‘Oh, my God, this is like my family,’” she said, adding that her company did not anticipate that the movie would be a big hit because it was in Thai.

“There was no way we would ever foresee the conversations around it,” she said.

In Manila, Ruby Ann O. Reyes, the vice president for corporate marketing for SM Supermalls, said her firm’s movie theaters distributed tissues to moviegoers. Employees were also on hand in the theater to give out more tissues during the “tear-jerker parts.”

“Filipinos love to have real-life lessons from every movie they watch, such as taking care of your grandmother and saying sorry while she’s still alive,” Ms. Reyes said.

Ian Jeevan, 27, a financial consultant in Singapore, said the movie reminded him of his relationship with his grandmother. He uploaded a TikTok video of himself choking up, with the caption: “Running over to hug my grandma now!!”

Muktita Suhartono and Rin Hindryati contributed reporting.