This kanji character is rarely used on its own, but is often found combined with other characters.
For example, 関西 (Kansai) and 関東 (Kanto).
Since ancient times there has been a road from Tokyo (the current capital) to Kyoto (the former capital). At the mid-way point there used to be a large gate. This led to people thinking of places in Japan as being either "West of the barrier" 関西 (Kansai), or "East of the barrier" 関東 (Kanto). To this day, the distinction still exists, and there is still a fair amount of good-natured East-side/West-side rivalry.
Although this character refers to a barrier, it is found in words related to "connection" such as 関係 "relationship" and 関心 "concern/interest".
It seems as if, as far as the Japanese language is concerned, a boundary is not only something that can form a barrier between two things, but also something which can connect two previously unrelated things.
Did a series of illustrations of some of my favorite Pokemon Glitches in the first three gens! The Mew Glitch very nearly beat out Missing No., because that's actually my favorite Gen 1 glitch, but Missing No. is just so visually iconic, I had to lol