User blog comment:Inept Wiki User/Cosmos in the Lostbelt: Post-Prologue, Pre-Anastasia Information & Speculation/@comment-4616657-20180327163507/@comment-34352073-20180327180412

It's possible that Rider could be William Adams, but I wouldn't bet on it. I mean, he has what looks like a wooden katana and is chained to it too, so maybe? There is the shield-looking thing on his back to be considered, though.

His armor, to my eye at least, looks closer to something a mainland European would wear. Sailors also aren't known for their heavy (plate in this case) armor. On closer inspection his armor reminds me a lot of that of some Greek mythos Servants, in the style of Achilles and maybe Hector. Got no clue what he might be riding though.