What's something with nine sides? Just add a drop and you'll have something that's almost a circle.
Do you know about the adorable cat Maru? If not, you should check it out. May seem like a distraction, but if you come back knowing the reading for this kanji, then it's totally worth while.
When you think about a circle, think about Maru all rolled up in a little circle, being super adorable. Don't tell me it doesn't melt your heart just thinking about it.
Alternatively, you could also look at this kanji and think of Maru inside of a box, with his little tail sticking out of it. Whatever works best for you, just get yourself to "Maru."