Killing two trees with a jackhammer is expressly prohibited. Don't get me wrong, you can rip up one tree with your jackhammer, but not two.
The person who decided to prohibit jackhammering two trees is the King (きん) of England. He's the only person who's able to prohibit certain things, so it had to be him.
Currently there are no similar looking kanji which exist in the WaniKani learning system