Crossovers that Should Be: Super Double Bonus Round

[deadpan29]

Jinx999 wrote:

---

The Neogi "trade" fleet moved into orbit. It was a previously unknown crystal sphere, but the world beneath was a typical earth body, if with more ocean than usual. And clear signs of cities.
An inhabited world with no knowledge of spelljamming was always a good source of slaves and wealth.
. . . . . .
On the ocean below a young woman looked up through her telescope, watching the new lights in the sky and ignoring the antics of her crewmates.
"Hey, Nami! Food's up."
Spelljammer - One Piece.
And they used to think Tinker Gnomes were a menace.

A crossover I've been trying to envision for a while is One Piece and Tenchi Muyo GXP.  World of pirates meets interplanetary pirate bait/trap. 
Unfortunately, I can never figure out how to work the relative power levels.  Seina with his full battle harem, Washu-tech cruiser, and god-machine mecha should curbstomp even the more outrageous powers of One Piece.  Without that backup, he seems terribly fragile.On the other hand, Seina is tough enough to have survived his years of bad luck, plus the GP nanomachine combat enhancements.  Not to mention, how does anyone beat the bad-luck trump card?  
----------
No, I don't believe the world has gone mad.  In order for it to go mad it would need to have been sane at some point.