A Taiwanese man who has lived in Japan with his male Japanese partner for nearly a quarter century is now on the brink of separation not because he has fallen out of love but because he faces deportation for overstaying his visa.

Hoping to continue living with his partner, he has filed a lawsuit with the Tokyo District Court to nullify the deportation order.

His lawyers argue he should be granted special permission to stay in Japan in the same way foreign partners in heterosexual couples are sometimes allowed to remain on the grounds they have led stable lives with their Japanese partners.

“I have lived secluded from society for more than 20 years,” said the Taiwanese man, who is called “Mr. G” by his supporters to protect his privacy. “But my Japanese partner and I have supported each other as a family.”

Mr. G, in his 40s, met his partner, now in his 50s, while visiting Japan and started living with him in 1994 before eventually overstaying. He was diagnosed HIV-positive in 1995.

“We have pretended to be brothers, although we do not look alike,” he said. “I was tortured by a sense of guilt when I was young, as homosexuality was not a socially accepted idea in Taiwan. My family told me to receive medical treatment to ‘cure’ homosexuality.”

He was arrested last year for illegally staying in Japan and is prohibited from working as he is now on provisional release status.

“Mr. G and his partner have maintained a stable relationship for a long time. He also needs to receive treatment” for his medical condition, Yuki Maruyama, a lawyer representing him, said, stressing the necessity of granting him special permission to stay.

Yasushi Nagano, his other lawyer, said: “Considering his long-running stable life in Japan and his health, he should not be forced to separate from his partner. Their relationship should be protected by the constitutionally guaranteed equality before the law and the rights to the pursuit of happiness.”

The government argues that the deportation order is legitimate.

Several same-sex couples with Japanese and non-Japanese partners gathered for a recent meeting in Tokyo to support Mr. G. Many of them share the concern that non-Japanese partners may face deportation some day if their visas expire, even though they see themselves as de facto families.

Among them was Ai Nakajima, who lives with her German partner, Kristina Baumann, whom she met in Berlin six years ago.

While Baumann currently works at a hotel, Nakajima said: “My partner may face the threat of deportation if she loses her job. We are always haunted by such concerns, although we hope we could continue living together in Japan.

“We are recognized as partners in Germany, but our relationship means nothing here,” Nakajima said. “We hope same-sex marriages or same-sex partnerships will be legalized soon so foreign same-sex partners will be granted resident status.”

More than 20 countries around the world, including the Group of Seven major economies other than Japan, have introduced a same-sex marriage or same-sex partnership system.

Regarding the case involving Mr. G, Ken Suzuki, a law professor at Meiji University, said, “It is discriminatory treatment on the grounds of sexual orientation.”

Taiwan’s constitutional court ruled this year that same-sex marriage is a guaranteed right, making Taiwan the first Asian jurisdiction to allow such unions.

In Japan, meanwhile, six local governments, including two Tokyo wards and Sapporo, recognize same-sex partnerships, ensuring couples the same treatment and entitlement to local services as married couples.

Prior to these developments, the Tokyo High Court ruled on a high-profile case in 1997 that it is unforgivable if administrative authorities do not understand or are not interested in the rights of gay people and that they are required to give due considerations to minorities, including gay people.

“It is needless to say that immigration authorities are covered in this ruling and that they are also required to ensure the rights of minorities,” Suzuki, also an LGBT rights activist, pointed out, requesting authorities to be thoughtful of the situation of Mr. G.

“It is unacceptable internationally that Japan does not recognize same-sex partnerships,” he added. “I expect Mr. G’s landmark legal fight, combined with the local moves, to lead to improving the rights of lesbians, gays, bisexuals and transgenders.”

Estranged from his Taiwanese family, Mr. G considers Japan the only place he can live.

“Legal rights of LGBTs have not been considered and the existence of same-sex binational couples has been ignored,” he said. “I hope same-sex international couples will be treated equally with heterosexual ones.”