Okay this has been KILLING me, I read this story so long ago and loved it. I don’t remember that much though, so sorry in advance.

I’m looking for a yaoi/bl manga that:

-Is about an uke with memory loss of some sort
-Is a sequel to another series
-Has a lot of action-oriented plot, is not purely romance. Fight scenes, etc. I think that later in the story they were involved with secret agents or criminals of some sort. I think they were on a ship for a while.
-Has a light-haired uke
-Has great art
-Is not recent. From 2012 or 2013 at the very latest.

I think the uke was given shelter by the seme at some point in the beginning because I remember them staying at his apartment. Sort of gave me Mission Impossible vibes with the amnesia. I know the author loved cliffhangers. And I remember that you could read it online but some (rather large) sections of the story were only accessible if you payed for them.

I know this isn’t much to go on! It’s been bugging the hell out of me, though, so thank you in advance to anyone who can point me in the right direction.

Reading your summary made me think of Yellow although I don't remember if it had memory loss. I do remember it had quite some action scenes.
Also, do you remember where you might've read the manga?

Dang, Yellow sounds so similar but the art style was different. And unfortunately I don’t remember for sure, but I think it may have had its own domain. I remember that it was a bit hard to find.
Thanks for the response!

Quote from DarkQueenOfAustin

Dang, Yellow sounds so similar but the art style was different. And unfortunately I don’t remember for sure, but I think it may have had its own domain. I remember that it was a bit hard to find.
Thanks for the response!

Yes, yes, something very familiar, I can not remember ( 😕

Hi! I'd like to help you find the manga if possible.

Here are some minor suggestions that don't really fit everything you are talking about, but have similar themes in case maybe it is what you were thinking about:

Moritat
G-Defend
Madness
Koujitsusei no Tobira
Wild Adapter
Silver Diamond
From Dusk till Dawn

*Note: I haven't read any of these, but have searched around thru tags, so I'm sorry in advance if these are completely off.

If it is so that none of these are what you are looking for; are there any specifics you have in terms of if it was Japanese, Korean, Chinese, etc or if it was webtoon style(scrolling down the page) or manga style with page to page w/ multiple panels?