The Amaterasu Lore Makes no SENSE AT ALL.

[Lord Caedus]

So your problem isn't that the ship is exclusive to Samura, it's that it is called a liner and that OS&C can't use it, even though it's a liner? Samura doesn't want to sell them to outsiders, if you ask them nicely they might let you have one, it'd be about the easiest request ever.

EDIT: Just remembered that OS&C is very obviously not able to operate in Kusari for the exact same reasons Samura restricts access to their ships, they want to make the money themselves, not let some other company make it.

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