It's not the same language, just the script. Someone brought Japan the newfangled concept of language scribbled on objects some time between 3 to 5 century AD,

It's not the same language, just the script. Someone brought Japan the newfangled concept of language scribbled on objects some time between 3 to 5 century AD, and the Japanese nobles adopted that Chinese written language for record keeping and transcriptions. There was already the Japanese spoken language, and nobody in Japan had personal connections to Chinese people(having a rough sea between two countries tend to do that), so Japanese interpretation of "Chinese language" and its characters is completely its own thing - in China the script is called "Hanzi", pronounced like "kHang-zeh", rather than "knanJI" in Japanese. With the "Simplified" form created by Chinese communist movement in the mid 20th century, there are currently at least 3 major branches of Chinese scripts: the OG "Traditional" kind, its alternate "Simplified" form, and the Japanese "Kanji" - plus (deprecated)Vietnam Chunom variant, (minor)Hong Kong PRC-traditional variation, Korean Kanji w/o post-war Japanese simplifications, etc. Each ... has slight variations and significant overlaps. Unicode technically supports a lot of those, some by co-mingling, some by rubberstamped-in duplicates, some by IVS(Ideographic Variation Sequence). To realistically support all languages in one font or app, there need to be distinctions based on languages rather than bandaging hand-wavy "it's all kanji" approach(the word kanji is Japanese, for starters), but the Unicode Consortium is not doing that.