Are Darkin weapons or are Darkin in the weapons?
Kayn's champion reveal says >He audaciously wields the sentient darkin weapon Rhaast, undeterred by its creeping corruption of his body and mind. There are only two possible outcomes: either Kayn bends the weapon to his will... or the malevolent scythe consumes him completely, paving the way for the destruction of all Runeterra.
but the description of his passive says >Kayn wields an ancient weapon and fights the darkin within it, Rhaast, for control.
And, for good measure, I'll mention Eduard Santangelo's Vastaya Journal which referred to Darkin as >Those horrifying, sentient weapons known as Darkin.
We don't know that much about the Darkin yet. If they're living weapons, were they manufactured for a war? Or is living weapon just a phrase used because they're good at killing, meaning they're basically just monsters? My guess is that the reason these quotes seem odd is because we don't fully understand Darkin yet. I am also guessing that Darkin are living weapons within other weapons.
Can a Darkin not be in a weapon? I'm thinking of Shen's spirit blade. Is that a blade that is a spirit? Is it alive? Is it a Darkin (a weapon-within-a-weapon) that is not within a weapon, and is just a living weapon? (Of course, if it is a living spirit that is a blade, it doesn't have to be a Darkin.)