Every time he woke up to the flashbacks of horrific killing scenes, he shut his eyes tight and tried to turn his mind away from something he no longer wanted to think about.
But Makino, 84, also felt he had to speak out about his wartime experiences to as many people as possible during the final years of his life.
"These were nothing but living-body experiments," Makino said at a hospital in Osaka, making some of his last comments before he died earlier this year.
"My captain combat-surgeon often showed us human intestines, and said this was the liver and that was that and so on," he said.
"He did that to train us. The captain said if he died, we would have to take up a scalpel to conduct the operations instead of him."
Makino, a low-ranked medic deployed to a Philippine island during the final years of World War II, began making his striking statements on Japanese war atrocities in public just last year.
He was regarded as the first former Japanese soldier to have been stationed in the Philippines to speak of vivisections on hostages and his remarks caused some controversy as historical memory remains a point of simmering friction between Japan and the countries it invaded. Nationalist Internet sites launched a campaign branding Makino a liar.
Makino said what he experienced was not systematic atrocity, but rather soldiers' desperation during the disorganised, last-ditch struggle of a nation on the verge of defeat.
It was one year before Japan's surrender when Makino landed on the island of Mindanao in August 1944. He was assigned as a medic in the 33rd coast guard squad of about 20 soldiers who were in charge of detecting enemy airplanes.
His squad joined a landing force of some 1,500 troops on the fabled Yamato, once the world's largest battleship which US bombers sank later in the war. "The Yamato was such a huge ship that it could not easily find a suitable port," he said. "So the ship anchored in the middle of Manila Bay and we dispersed to a variety of destinations in the Philippines."
Soon after arriving at the Japanese military base at Zamboanga on the western tip of Mindanao, Makino found himself and his unit cut off from headquarters, with the situation growing worse by the day. They received no military supplies or orders, let alone medical packages.
The main enemy facing the small Japanese squad were the guerrilla bands formed by local Muslim Moros, who constantly threatened their station, he said. "We were told the Moros were such cruel people that they attacked enemies with spears, and we actually rescued some people assaulted by them."
Naturally, he said, almost all the hostages they captured were Moros. "We were supposed to keep them alive in captivity, but it was no problem if we 'disposed' of them, in the beheadings the Japanese have become infamous for." He remembered at least 50 hostages being killed.
The frail old man recalled that many others were kept alive as human guinea pigs for his superior combat doctor, who wanted to show young medics like himself how to conduct surgical operations.
"We first anesthetised them we usually used injections or oxygen gas. Then they passed out in a few seconds." The combat doctor would tell him to watch as he sliced open a hostage's stomach, a scene that Makino says made him so ill he couldn't eat or drink for days afterwards.
"When cooking chicken, the doctor would get amused and say 'oh, this is just like human intestines'."
But Makino said he eventually became accustomed to what he had to do. "I was desperate. I didn't want to do anything like that if possible. But I had to follow the orders of my superior as a military man, or I'd have been beaten up."
He could not put a definitive number on how many of the 50 people the unit killed were vivisected or how many of the operations he took part in.
He did say he could never forget those days on the tropical island and even six decades later he could barely talk about his experiences without breaking down. As he spoke, he lowered his eyes and said he felt the most profound guilt over the way the bodies were handled afterwards.
The Japanese made Moros dig holes in the ground, he said, and then they hurled in the bodies with the stomachs still open. "The mud got in all over the stomach. My captain said there was no need to close the wounds because that would just be a waste of suture thread."
Makino's confession revives memories of Imperial Japan's "mad scientist" Lieutenant General Shiro Ishii, who led the infamous Unit 731 in northeastern China, where the Japanese made their colonial base of Manchukuo and conducted germ warfare tests on prisoners. Ishii is believed to have attempted the mass production of biological weapons by testing deadly germs such as anthrax, dysentery and cholera on prisoners of war, mainly Chinese, and dropping plague-carrying fleas and rats on their villages.
Makino said his unit in the Philippines did not have any organised plan and that it did not test plague germs.
"It was a one-off thing," Makino said. "We didn't take data or anything."
Another veteran, one of only a handful surviving from the Philippine battlefield, said the final days of the war were so desperate they did whatever they thought necessary just to survive.
Yoshihiko Terashima, 86, a former naval chief commander, said he did not commit any living-body experiments himself but added: "That could have easily happened."
"It must have been natural for military doctors to come up with the idea of using whatever they had for tryouts in such destitute situations," he said.
"They had no medicine and no supplies, so then of course they would have had to come up with ways with whatever they had. And they must have done the same thing to injured Japanese soldiers as well."
He contrasted the situation in the Philippines with that in northeastern China, then known as Manchuria.
"There (in Manchuria) Japan was winning the war. During the time of Makino (in the Philippines) we were losing it."
The Americans landed on the Philippines' main Luzon island in January 1945 and within six months declared victory. An estimated 218,000 Japanese soldiers were killed in the battles on Luzon island alone.
Like many Japanese soldiers, Makino and Terashima each fled into the jungles.
At his home in a Tokyo suburb, with cabinets full of war documents and a rolled-up map of the world lying on the floor, Terashima recalled the destitute conditions that he faced while fleeing from US attacks.
"When you holed up in a cave at night, you see huge rats crawling up on the faces of dead bodies, eating the eyeballs," Terashima said in a firm voice.
"So we took an iron helmet to catch them and ate them.
"Those dying just lay on the ground, living a few days by eating the maggots that were infesting their own faces."
In later years, both Makino and Terashima repeatedly returned separately to their former battlefields to collect the remains of Japanese soldiers.
Makino travelled back and forth between Japan and the Philippines more than 10 times, taking everyday supplies like rice, pencils and clothes to needy residents of Mindanao.
"I've done it out of a quest for redemption," Makino said.
Makino said the past haunted him for years, so much so that he hesitated to marry. "I would tell people that I had reasons for not being able to marry."
It took him 10 years to make up his mind to marry a friend's sister, but said he could not talk to her, or anybody, about the surgical killings committed by his unit in the Philipppines.
"It was cruel, too cruel to talk about it to a woman. My wife might have thought I was such a cruel person. That's what was in my mind.
"While she was with me, I just didn't want her to know about it," said Makino, who kept a monochrome photo of her on his bedside at the hospital where he died in May.
Makino said her death more than three years earlier freed him to talk publicly about the experiences that haunted him.
"You have to talk when you know you have done something guilty.
"We lost the war because we deserved it," Makino said with bitterness. "We didn't have enough soldiers, enough arms nor enough bullets. We didn't have enough of anything."