Square plus one equals sun

square plus ten equals ?

Solve this equation – what should appear instead of the question mark?

This funny puzzle is from NEC’s とんちクイズ 2011 wall calendar, September. Every month has a new quiz, often based around word plays, presented by a little monkey called Gozaru. The quizzes are easy enough for most Japanese children to solve, but usually rather hard for me. You will need to know some basic Japanese to be able to figure this one out.

Let me know in the comments if you have the solution or need some hints!