Sorry for using romaji. I'm referring to the sounds made when a word contains a kana sequence like 「ない」 or 「たい」or 「さい」 「かい」
I've read that the two together sound like the word "pie" sounds in English. I've also read that both sounds are fully pronounced. This seems like a contradiction to me? Does it vary from word to word? Does it vary from person to person?
In this YouTube video of 「ちいさい」being said by two people the word sounds to me like it rhymes with English "pie."
https://m.youtube.com/watch?v=4-BvtEisTU8
In this song video, 「せかい」 sounds like it has two distinct sounds at the end. (I've linked to a spot right before the word is sung.)