(CNN) It might just be the most bizarre criticism of a US ambassador in recent memory.

Harry Harris, Washington's envoy to South Korea, has been subjected to heated vitriol on social media and by anonymous netizens for his mustache.

That small piece of facial hair has, as Harris put it, "for some reason become a point of some fascination here in the media."

"If you watch social media it's all out there," Harris, the former head of US Pacific Forces, told a group of foreign reporters Thursday.

On the surface, the critiques border on ridiculousness. It's just a small patch of hair.

But Harris' 'stache has sparked discussions on topics much bigger than the ambassador himself: the still-raw emotions among many Koreans about the legacy of Japanese occupation; the prevalence of racism in such a homogenous society; and cracks appearing in the future of the decades-old alliance between Seoul and Washington as the two sides attempt to reach a deal on how to cover the cost of US troops stationed in South Korea, amid reports that President Donald Trump demanded a 400% pay increase.

The gist of the criticism is that with the mustache, Harris resembles the reviled Japanese leaders who ruled the Korean Peninsula with an iron fist during the Japanese occupation.

Some of Japan's most prominent wartime leaders -- like Hideki Tojo, the Prime Minister who was later executed by a postwar tribunal, and Emperor Hirohito -- had mustaches.

Under Japanese rule, many Koreans were brutalized, murdered and enslaved. It's still living memory for elderly Koreans and remains a highly emotive subject in both North and South Korea.

In recent years, issues relating to the war have become a point of contention between Japan and South Korea. Fierce debates have broken out over the status of "comfort women" -- Korean women forced into providing sexual services for Japanese soldiers -- and whether Japanese corporations should pay individual reparations for Koreans who were forced into labor.

Hideki Tojo takes the stand for the first time during the International Tribunal trials in Tokyo in 1947.

Harris was born in Japan to a Japanese mother and American father, who was a Navy officer, and some online commentators have pointed to Harris' heritage along with the mustache in their criticisms.

But Harris isn't Japanese, he's a US citizen. And calling him out for his Japanese ancestry would almost assuredly be considered racist in the United States.

South Korea is a homogenous society without racial diversity like the United States. The CIA World Factbook doesn't even list other ethnic groups living in South Korea on the country's page, instead just referring to the country as "homogenous." Mixed-race families are rare and xenophobia remains surprisingly common.

Harris, who has dedicated years of his life to the service of his country, said in an interview with the Korea Times in December that the only times his ethnic background has come into play was when he criticized China for its actions in the South China Sea, and recently, in South Korea in connection to his mustache.

"I understand the historical animosity that exists between both of the countries but I'm not the Japanese American ambassador to Korea, I'm the American ambassador to Korea," he said. "And to take that history and put it on me simply because of an accident of birth I think is a mistake."

Harris said he believes the argument that he resembles Japanese wartime leaders "cherry picks" history. He cited two mustachioed Korean independence figures, Ahn Jung-geun and Ahn Chang-ho, as proof.

Members of Seoul Jinbo, a civic group of progressive activists, hold a rally near the residence of US Ambassador to South Korea Harry Harris in Seoul on November 11, 2019. His face is superimposed with a cat because he joked on Twitter that his cats were OK after a group of students broke into his house.

"I didn't grow a mustache because of my Japanese heritage, because of the independence movement of Korea or even because of my dad. I grew it because I could and I thought I would and I did," he said.

Harris explained that he grew the mustache to mark a new phase in his life, after he retired as commander of the US Pacific Fleet and began working as a diplomat.

"I couldn't grow taller, I couldn't grow hair on top of my head, but I could grow it on front of my head and so I did that. Nothing more nefarious than that, I wanted to have a change," he said.

When asked whether he would shave the mustache to help smooth relations, Harris told the Korea Times that someone would have to convince him it would benefit the US-South Korea bilateral relationship.

"I am who I am. All I can say is that every decision I make is based on the fact that I'm American ambassador to Korea, not the Japanese American ambassador to Korea," he said Thursday.