The controversy is an embarrassment for Kishida as he prepares to host Group of Seven summit in May. Japan stands out as the only nation in the group that does not recognize same-sex marriage or equivalent rights.
Arai made the remarks last Friday during a so-called off-the-record briefing with reporters. Earlier in the week, Kishida had shared his concerns about same-sex marriage and its potential impact on family structures during a speech to the Japanese Diet.
Arai briefed reporters at the prime minister's office that night. Asked about his views on same-sex marriage, he replied: "Negative. All the secretaries to the prime minister are against it.
"Talking about myself, I don't want to see same-sex couples. I don't like them if they live next door. If Japan recognizes same-sex marriage, some people will abandon the country."
Arai later said that he would retract his remarks if they were regarded as discriminatory, and offered an apology.

Kishida acts swiftly
The following day, the prime minister sacked Arai, describing his comments as "outrageous." "I have said I will aim for a sustainable and inclusive society that recognizes diversity. Arai's remarks are totally incompatible with those policies of my administration," he said.
Arai was one of Kishida's eight executive secretaries. He was in charge of coordinating economic and industry policies. He oversaw public relations and media affairs.
Appointed in 2021, Arai accompanied the Japanese leader on most of his overseas trips, writing speeches and media conference notes.
Shockwaves at home and overseas
The international reaction to the controversy has called into question Japan's approach to human rights.
Reuters highlighted how Japan is at odds with other G7 nations in terms of its same-sex marriage stance.
The BBC reported the traditional roles of men, women and family are deep-rooted in Japan. It also noted the Kishida administration's low approval rating after a series of political scandals, with Arai's dismissal dealing another blow.
Opposition lawmakers in Japan described Arai's comments as offensive, old-fashioned and out of touch. Some said they were concerned about the prime minister's office approach to human rights.
A support group for sexual minorities visited the prime minister's office on Monday to protest the remarks, which they say deeply hurt those involved. They met with Mori Masako, a special advisor to Kishida, and submitted a request to the prime minister for legislation to allow same-sex marriage.

Kishida and same-sex marriage
Kishida told a Lower House budget committee meeting last week that same-sex marriage requires careful consideration as it represents a change in how family is regarded, as well as values and, more broadly, society as a whole.
Arai's remarks were triggered by Kishida's own speech in the Diet about his reluctance to enact legislation on same-sex marriage. The prime minister's approach takes into account views held by conservatives within the ruling Liberal Democratic Party. But with the issue becoming a human rights concern, pressure is mounting for legislative change.