Japanese is derived from Chinese
They can't pronounce their "r's"
No Japanese sounds were borrowed from Mandarin. Mandarin is a bastardized language pigeon of Manchu and Chinese, rather than a pure Chinese language. The Japanese onyomi come from the languages of different ancient Chinese dynasties such as Wu, Tang, Han. Nothing from the Qing at all.
certain (actually, lot of) words were derived from Chinese.
Question is rather, which Chinese?
Late Ming/Qing-era Mandarin or Ancient Chinese?
Because ancient Chinese sounds like something out of Tolkien's novels. And they actually rolled the 'r' like no tomorrow.
Kanji on-yomis are classified among lingusts into sounds from the Tang dynasty (Tou-On), sounds from the Wu dynasty (Gou-On) and sounds from the Han dynasty (Kan-On). Since the peak of the Sino-Japanese cultural exchange happened at the time of the Tang dynasty, most of the sounds belong to that era.
>japanese is derived from chinese
Not him, but he probably meant it like how profoundly English has been influenced by French that you could say it derives from French. It may be dumb to word it like that, but to autistically argue semantics pretending (I hope) that you don't get it is just as bad or worse.
Shanghainese and other Wu dialects often sound similar to Japanese dialects as well. Min and Wu dialects have had fewer sound shifts than Mandarin. There's quite a bit on it here: https://en.wikipedia.org/wiki/Sino-Japanese_vocabulary#Phonetic_correspondences_between_Modern_Chinese_and_on.27yomi