The soul of a ship girl...

...is a very fragile thing.

Just one tiny little mishap...

...and the balance will immediately collapse.

If the soul of the ship is too strong, the girl will be pulled into the abyss, and change into a demon.

And if the soul of the human is too strong, her rigging will be purified and disintegrated, thus depriving her of her ability to fight.

The ship girl is always in between.