Diamond Dust (KANG Hyung-Gyu) - Deals a little with it.
Again!! and Kimi ga Waratta - It's kinda like Heptagon.
Orange (TAKANO Ichigo) - a letter containing the female lead's diary is sent to her.
Kareshi Kanojo no Jijou - the male lead can't forget his past.
Skip Beat! - Ren's memories.
Kagen no Tsuki - Female lead's memories.

Her memories are mixed with another person's

"A Lady Needs Time To Prepare. Even If It Takes A Year, A Gentlemen Must Wait." ~ Wilhelm Mölders(Emma)

^^ Wow. Thanks, everyone for the variety of recommendations. Some of them may have been repeated in this thread, but that's alright.

Quote from Tripitaka

Well, the original thread isn't mine but I decided to pick it up with some other members. We're still working on it in order to give it a new, revised form.

By the way, have you checked the category lists about memories?

I see. Wish you good luck with it. ^_^ (I don't think there's much I can add to that thread since anything I read "educational" should have been mentioned. Hmm... Although, I could throw "Tic-tac-toe Joe" in there just for fun.... Hehe.. Just kidding!!)

As for the category lists, I did sort through some categories, but there are some manga out there that won't have "amnesia" or "memory loss" tags attached to them when they actually have an element of them somewhere within the story. Edit: And I guess, I keep looking for ones with male MCs having memory-related issues and less with female MCs.

@ anngee:
.... I never considered "Skip Beat" as a contender, but you do have a point about Ren's "dark" memories of his past. This could also extend to Kyoko's own past, just a teeny bit.

• Looking for memory related manga/manhwa? -> click me
• Public webtoon list -> click me
  Zero-Sum manga fix status (-super thank you, admins-) -> http://bit.ly/1mTntim

2016 Update

It's been almost three years since this thread was updated. Since then, webtoons have really taken a hold on the internet, new manga/manhwa/manhua have come out, and an advancement in localization has shown up on Amazon.

Here's what I've found since the last time this thread was active.

Manga/manhua/manhwa/other

Reincarnation no Kaben - relying on the memory of the "abilities" your previous life had in a form of "talents'. But, there are also flashbacks....
Kataribe no List - I recently caught up to finishing this. To explain the memory connection would be a spoiler.
Bato Rabbits - From the creators of 07-Ghost.... However, the true memory related stuff happens way beyond the first volume.
Saihate no Ao
Boku o Tsutsumu Tsuki no Hikari - the sequel to "Please Save My Earth". Will have to check out the sequel to this one.
Memory [Locked] - Vietnamese manga so there is no MU profile. Only two chapters released in English, because the creator needs a translator. ^^;
Toukyou Kushu:re - But to understand this, the first Toukyou Kushu needs to be read.
1001 Knights - It's shoujo! Not -ai or BL. The reason why there is an undertone is because of the

MC's soul and past life, which was female. So, you got a confused love obsessed genie, who's stuck in the past. =__=; Even I'm someone, who stays far away from -ai and BLs, but I'm willing to stick with this story because it's got potential and familiarity with the mangaka. The thing to really worry about is if Yukiru-sensei will be able to finish this story?

Gokurakuchou Dead End - Although, the one-shot dealt with memories a little, the first serialized chapter is making me think there is something more than what meets the eye with the MC.
Bloody Mary (SAMAMIYA Akaza) - Definitely not BL. The vampire MC has a bloody memory problem.
Fruits Basket Another - The sequel, which nose dived immediately towards the troubled past of the MC. So, she keeps reflecting and reflecting.... The first FB had lots of flashbacks, so no doubt, this one will be of a similar vein?

Webtoons - regardless of language. Original English ones, I linked directly to Webtoons.

S.I.D.
Dalsez
Kot Dream
TRUMP

Knight Fantastic Knight - Chinese webtoon. No MU profile, I think? Well, the girl MC gets

constantly threatened that should she fail, the game will restart and everyone's memories will be wiped. I do think/theorize that there is a little more to this. Particularly, with the real world. The only thing about this story is that, yeah, it's like the MC was thrown into a harem game, plus, she is a cry baby/weak female. But, she does go through the shoujo character development phase. So does the main male lead. Despite all the shoujo cliches, I'm being very tolerable towards them and the harem. I'm here for the big mystery between the real world and fantasy world. This comic is actually based on a light novel.

Magical Exam Student - This is very LIGHT on the memory thing, because (major plot spoiler) ->

all the "future" involved characters had to witness their time being repeated over and over. So, their past selves keep forgetting they already went through that year. Imagine having to repeat 12th grade again and again, without ever remembering..... But, I do recommend this story if you're up for a funny shoujo parody with a deeper sad meaning behind its story.

Hero After Hours
THERIANTHROPE
Kings Folly
SPLIT

If I remember any that I forgot or find more, I will come back directly to this thread to add them in. So, this may be the only bump for this year. 🤣

• Looking for memory related manga/manhwa? -> click me
• Public webtoon list -> click me
  Zero-Sum manga fix status (-super thank you, admins-) -> http://bit.ly/1mTntim