There are some nouns that take the ending -у (locative) instead of -е (prepositional) after the prepositions в, на, like год, лес, сад.
Question: Is there any such noun which does not end on a consonant?
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e.g. край, brink
на краю, at the brink
Note: There are different phonemic theories built around Russian; some of them consider the sound "й", or / j /, the jod, to be a semivowel. See p.76 here.
"the locative case has largely lost its use as an independent case and became the prepositional case, which is used only after a preposition. The latter is not always used to indicate location, while other cases may also be used to specify location (e.g. the genitive case <...>)."
There are more examples there.