“Akuto the Eel? You do realize that boug sword tempered my strength – in revitalizing me, it slowed me down… As for Watch and Learn… Taking on the moves of others – made me weaker by design.”
Looks like, she muttered.
Looks like – I was wrong.
Nanami Yasuri – stood up.
“I was wrong.., to try and live a little longer – to fight you head-to-head in my condition.”
“Huh?”
Watch and Learn.
One would think – the skill would make a person stronger.
That it would mean the acquisition of additional strength.
However –
A genius like Nanami Yasuri.
Took on the skills of others – to become weaker.
In order to be weak.
A weaker being.
Governing – her strength.
That she may live.
Nanami Yasuri watched and learned not to increase her strength – but to survive.
And thus – she watched and learned voraciously.
Maniwa Ninpo.
The monstrous strength of the Itezoras.
The necromancy of the Sacred Guardians of Mt. Shirei.
The Gokenjiryu of Seiryoin Gokenji Temple.
And yes.
Even the methods of the Kyotoryu!
“S-Sis…”
No wonder Akuto the Eel didn’t suit her.
That it seemed like a bad fit – as fitting as it seemed to be.
The Mutant Blade, the work of Kiki Shikizaki, inarguably revivified Nanami – but only because it contained her strength.
To Nanami, Akuto the Eel worked as a handicap.
A handicap she needed – to survive.
To make her weak enough.

Katanagatari Omnibus 3, Page 84