That’s not it, but thanks for the guess, that was a really interesting one! 
I can confirm that there is a character from Japan, but it’s not him.
Since the current version of the game is severely lacking in repeat character descriptions, I’ll copy/paste an excerpt from his first appearance here as a refresher:
Kauê description
Behind you, a voice calls out, and you turn to see a young man of short stature standing in the doorway. His vibrant russet skin hides toned muscles. His bright orange hair somehow stands upright, looking almost spiky, and glows with a vivid warm light.
He laughs breathlessly and kneels. You suddenly notice that his feet are pointing backwards, giving his movements a unique quality.
“Hey! Come back here!”
You hear quiet hoofsteps coming from behind a wooden display, and a friendly peccary soon appears. She happily hops into the man’s arms while he beams at you.
“Hahaha, sorry about that! I’m Kauê, and this is my sister Kauane!”
She grunts enthustiastically as he tousles her hair. Aïssatou peeks out of the stockroom to check on the commotion and waves with a friendly smile.
I know of a few other characters you’ve definitely met, so I’ll throw those in too in case it can help:
Monday regulars
You’re casually stocking some shelves when a distant high-pitched voice breaks your focus. It quickly gets louder and the door soon opens, revealing a woman and a boy with beautiful russet skin and smooth dark brown hair.
Her gait is unusual, and you immediately notice that she seems to have no feet — another glance reveals that her heel is in the front and her toes are pointing backwards towards the doorway. Flaps of skin stretch between her body and her arms; the latter end in elegant long-fingered hands whose palms face away from each other.Your ears can suddenly make out words in the child’s excited babble.
“And then Ligaya said that she-”
“Just a moment, honey.”
The boy grows quiet and stares at you, wide-eyed. She smiles apologetically.
“You must be the new assistant; it’s nice to meet you. I’m Minviluz, and this is my son Bayani.”
(Just realized I apparently love the colour “russet” so much that I used it for 2 characters in a row — and it happens to be the two with backwards feet!)
~
Friday regular
As you set down your watering can, a tall and thin man slinks in through the front door. His beautiful long and smooth hair is almost as fair as his skin. You approach him and notice that he is soaking wet. On his back is a beautiful, ornate, eight-stringed fiddle.
“
<<if new Date().getHours() >= 7 and new Date().getHours() < 19>>Good day!<<else>>Good evening!<</if>>I’m happy to finally meet the new assistant! I hope you’ve been enjoying yourself. I’m Åsmund…”
The next time you see him:
As you set down your watering can, Åsmund appears with a shy smile and a wave. Mindful of the puddles he’s creating, he sponges himself off with a small towel as he greets you.
~
Saturday regular
You’ve just finished your task when you hear a dull thumping coming from outside.
Thump… thump… thump…
Suddenly, the front door opens, revealing a handsome young man with crutches under his arms. His flowy white chiton highlights his healthy light brown skin, and his slightly curly hair is tousled by remnants of breeze as he steps past the threshold. Most notably, he appears to only have a single leg that ends in an extremely large foot.
You close the door behind him while exchanging greetings.
“Hello, I’ve heard about you! It’s nice to meet you! My name is Echekrates.”
He carefully sits on a nearby chair and grasps his crutches in his hands as he continues.
~
Aïssatou herself (various scenes)
You push open the door and are greeted by a cheerful voice.
“!السلام عليكم”
Your eyes are drawn to a figure in the center of the room. A prickling warmth makes its way deep inside your ears, and the unfamiliar sounds quickly become perfectly intelligible.
“Welcome to my shop!”
The woman smiles warmly as she approaches you, and you take a moment to examine her.
She is very short, and moves so effortlessly and gracefully that you could swear she was floating. Her skin is inhumanly white and seems almost pearlescent. Her tightly-coiled silver hair is woven into elegant and intricate braids.
When asking her about herself:
“I hail from Senegal! My people live beneath the hills there and enjoy a life of opulence. But I wanted to make something more of my time in this world, so I left my country behind and founded this sanctuary alongside my little friend Diégane. I started out as a simple apothecary, but nowadays I find myself doing a bit of everything!”
These guys show up after solving all the cryptic clues:
Aïssatou falls to her knees beside you and you look back towards the approaching chatter. This time you notice two pairs of feet slowly walking towards you. They’re accompanied by two pairs of hands that sway back and forth, one pair higher in the air than the other. There is silence for a few moments as they draw near, then a melodic female voice energetically yells out:
“Aïssatou! You have completed our challenge!”
And her letter…
"Mamadou, Seynabou,
I am ashamed that it has taken me so long to recognize the rights that you deserve.
Surrounded by other yumboes who never questioned their lifestyles, I remained blissfully ignorant of your struggles. I thought that simply not being cruel was enough. That the natural order of things should not be questioned. I thought myself kind and benevolent. But later on, even as I helped other beings break free of the chains of their circumstances, I had a blind spot in my treatment of you. I still felt entitled to your work. In truth we were always equals in every way that matters, and I wish I could have realized it sooner.
I was extremely hurtful in my carelessness, and I sincerely apologize…"Her voice slowly trails off. She looks up and quickly rubs her eyes, then slips the paper into the satchel and hesitantly holds the latter out towards Mamadou and Seynabou.
“There is more, if you’d like to read it… I’ve also left some acorns in there for you.”
~
Feel free to ask about anyone else too (though no pressure to keep guessing, of course)! 
If I did my job right, all of the characters’ names should point to their native cultures, so that can be a clue as well!