Yes. A balloon that was created to specifically survive an onslaught from Flandre for an entire week.
Canon states that Flan destroys by pouring her magic power into the weakpoint of an object, so it makes sense that a toy meant for her would need to absorb a whole lot of the stuff.
What makes you say that?...Well, there's the topic of its absurd sturdiness...That's an anticlimactic ending....Touche.but back when she was tidying up the books, this is what she said.On the final day, it popped, and disappeared.Well, considering that thing lasted a whole week against her "ability to destroy"...That monster...from the beginning, could it have been a gift to Flandre?