Following MINE"s remarks about China and Korea, many individuals began to look more closely at the source material, which upon second examination, contained elements of those very sentiments. As a result, several members of the voice cast and staff all resigned on Wednesday, resulting in the anime adaptation's cancelation.
The story in [New Life+] Young Again in Another World (Nidome no Jinsei o Isekai de) itself centers on a protagonist who kills 2,000 Chinese citizens during a war between the two countries that occurred shortly before World War II. The material views these actions as heroic and one of the reasons behind why the elderly soldier from that conflict gets reborn as an 18-year-old in another world. There's been debate in Japan, with one side viewing that the light novels are just a work of fiction, while others view them as inappropriate.
Japan Twitter users subsequently unearthed old Tweets from MINE, which referred to China as "bug country" and other hate-speech, include a few Tweets directed at both North and South Korea.
The controversy began last Thursday and in less than a week, the adaptation has been shelved.