Question

Does the Koreas have a border around the island?

Answer 1

The only border around the Korean peninsula other than the border between the North and South would be coastlines.

Answer 2

South Korea's only land border (to the north) is with North Korea.

North Korea shares a border (to the north and northwest) with China and Russia (along the Amnok and Tumen rivers).

The Korean Peninsula as a whole then borders China, Russia and all its adjacent islands.