The previous topic

そ～ is often used to represent something that has just been talked about. In writing, こ～ can be used instead, to describe something as if it really exists.

わたしが一番欲しい物は「どこでもドア」です。このドアを開けると、どこでも行きたい所へ行けます。
What I want most is a “magic door.” When you open this door, you can go anywhere you want.