So, what's the real reason for jellyfish?

Did you use something that looks like or is related to one?

Wha-?

I mean, you can write jellyfish as "水月" or "海月", right? 海月 (kurage, suibo), 海 (sui - sea, beach) -> 水(sui - water) -> 水月. Resulting 水月 can mean "moon in the water".

Your point?

...A pun? Fun fact: 駄酒落 (dajare, usually written as 駄じゃれ) - "pun" starts with 駄 as well as 駄目 (dame) - "lame", "useless".

Moreover, you have one more 月 there 月 (tsuki) - moon.

Ah, something got her.