Phonological Gain

[Nortaneous]

For the record, initial nasals were present at one time but merged with the corresponding voiced plosives (m > b and n > d)

Isn't this currently happening in Korean?

[linguoboy]

For the record, initial nasals were present at one time but merged with the corresponding voiced plosives (m > b and n > d)

Isn't this currently happening in Korean?

Not that I've ever heard. Final plosives merge with nasals, but only by regressive assimilation to [+nasal] segments.

[Seirios]

Japanese is said to have borrowed /-j-/ and /-w-/ under the influence of Old/Middle Chinese loans. I mean Japanese, originally with only a syllable structure (C)V, C being absent only possible at the beginning of morphemes, borrowed the syllable structure CjV and KwV, K being restricted to velars. Apparently those loans also introduced the word-level syllable structure VV, that is, two continuous vowels in one single morpheme (in this sense you could also say that it borrowed long vowels but Japanese is mora-based so the concept might not apply). Also it originally had /r/ and voiced consonants but they could not appear at the beginning of words, and the loans ended these restrictions. I'm not sure if it borrowed syllabic /n/ or developed it by itself. I think I've heard people talking about Japanese borrowing nasalized vowels (corresponding to Middle Chinese -ng) and subsequently losing it centuries later but I never saw resources confirming this.