The world radical and the world kanji are the same, but there is another really important meaning you need to know: generation.
Think of it this way: the world is just made up of many different generations of people, plants, and animals all getting along together.
It's your job to protect the world and every generation with your special saber (せい). It was given to you to uphold correctness, and you'll pass it on to the next generation when it's time. Then they'll watch out for the world when you're gone.
Currently there are no similar looking kanji which exist in the WaniKani learning system