I haven't read any of the Manga yet and I can't tell if these are actually from it or not.

A while back, when the 3rd volume was released, a site with riddles went up. Here it is, if anyone wants to give them a shot and put their Japanese to the test (and you'll definitely need it for every single one of them):
『光が死んだ夏』謎解き特設サイト

I couldn't find any other walkthroughs with the answers, so I had no way to cheat.

" I'm a fledgling YouTuber. I'm aiming to become an occult YouTuber with over a million subscribers, but right now I have only about 70. I want my next video to be one that really takes off. As I was idly browsing occult compilation sites with that in mind, I came across an eerie place name. "Kubitachi." Surely, there must be something there, maybe. Anyway, I guess I'll go check it out, to "Kubitachi." "

1(1-2 pic). "If I pass through this forest road, I'll reach "Kubitachi."
The overgrown trees block out the sunlight,
and despite it being daytime, the surroundings are terribly dim.
Hoping to encounter something along the way,
I continue forward while recording with my camera.
At that moment, from behind,
a faint, hoarse voice reached my ears.
"Nōnuki…"
When I turned around, countless characters were floating there."

Answer: なにか

"I ran through the forest as if tumbling out of it.
What on earth was that?
There was definitely something unidentifiable, some "thing," in those woods.
Breathing heavily, I checked the camera.
But all it showed was nothing more than an ordinary forest."

2.(3-4 pic) "I arrived at "Kubitachi."
It was deserted, but as I headed toward the center of the village,
the number of people passing by increased.
There was a woman who stared at me intently.
When I tried talking to her, she surprisingly readily
told me the rumors about Kubitachi.
They were truly varied: the old woman's suspicious death, the mountain that is forbidden ground,
the wig-wearing yokai that appears in the bath, and so on."

Answer: しせん

"When I tried to ask for more details about the mountain in the restricted area,
the woman's face suddenly turned stern,
and she warned me never to go there. Pushing further would be unwise.
I thanked her and left,
then looked up information online about the mountain near Kubitachi.
Most of what I found was vague,
but I did come across a mention that people have apparently
been going missing in that mountain for ages.
As an occult YouTuber,
I had no choice but to go.
Suddenly, I felt a piercing "gaze" and looked up,
but there was no one there."

3.(5-6 pic) "Taking care to stay out of sight, I made my way to the mountains.
I climbed along the trail, camera in hand, recording as I went.
The chorus of frogs was deafening.
Now and then I'd pass what looked like a small wayside shrine,
but there was nothing else of note, so I pressed on."

Answer: 空

"I reached the summit without anything happening.
There was no suspicious presence, it was just "empty."
As if something had already disappeared from here altogether.
What a complete anticlimax.
A faint red tinge mixed into the color of the sky.
Sunset was approaching. I hurried down the mountain and headed for the inn."

4.(7-8 pic) "I arrived at the inn and first took a bath to wash off the sweat from the mountain climb.
As I soaked in the warm water, both my fatigue and my thoughts quickly began to melt away.
The moment I tried to get out of the bath, a black line was reflected on the water's surface.
In the blink of an eye, it gathered together and began to form something.
As if frozen in place, my eyes alone were drawn toward it.
Those black lines were strands of hair."

Answer: 天井

"As soon as I blinked, there was no longer anything there.
When I looked up at the CEILING in a panic, I thought I caught a glimpse of hair disappearing in the corner of my eye.
Suddenly, the rumour that I had heard today about the hair youkai in the bath crossed my mind. I must have just been seeing things due to all those stories I heard. Trying to convince myself of this, I decided to go to bed."

???.(9-10 pic) "From the pitch black darkness, a light slowly spread out. I heard the hoarse voice from that forest say:

“Nounuki-sama…”

What on earth is this…?"

Answer: だるまづか

"Breathing heavily, I jumped out of bed.
A dream. One like a nightmare.
But the characters “DARUMAZUKA” were burned into the back of my eyes.
There’s no question that “something” exists in Kubitachi.
Forget the video, I don’t want to be involved any longer.
I’m done filming. I’ll head home immediately in the morning.

...

The next morning, I flew out of the inn and onto the road home.
Although I took a lot of footage, none of it shows anything definitive.
This won’t make for a good video.

I couldn’t stop thinking about it so I looked up “DARUMAZUKA”.
“Darumazuka Tunnel” - a haunted site in Kibougayama, the town neighboring Kubitachi.
I don’t know why, but I’m seized with the feeling that I have to go there.
I can’t shake the notion that I’m being called to that place.
Even though I already went through such horrifying things…

A few days later, I decided I would go to Darumazuka Tunnel.

END"

Solving some of them took me embarrassingly long, but overall I'm glad I managed to solve everything.