Pair
counter, noun, prefix
The kanji and the word are exactly the same. That means they share meanings as well.
そう
The reading you learned with the kanji is the same as the one used here. They're a pair, you know?
妹と私は二卵性双生児ですが、外見がすごく似ています。
My sister and I are fraternal twins, but we look very similar.