First, the simple basis for understanding the way Japanese think about the supernatural. Simply put, Shinto, which was the country's official religion and is the religion that originated there, is an animistic faith, with a strong tendency toward the personification of nature and objects. Second, Buddhism was the dominant faith in Japan for centuries, when the various shogunates tried to weaken the Emperor's power by strengthening the influence of Buddhism as a rival faith.
Why is this relevant? Shintoism personifies the dead and believes in the concept of living gods. The Buddhist tributaries in Japan generally believe in reincarnation. Both faiths create a belief that there are things in the world that exist alongside us that cannot be seen by 'normal' people. Both have a belief in life after death, and both have a concept of 'lingering' and 'ascension'.
Generally speaking, Japanese spiritualists hold to a belief (or so they say) that if you can see a spirit, you can effect it and it can effect you. It is vital to understand this before anything else when dealing with Japanese spiritualism in general. While the idea of ghosts harming or possessing those who can't see them isn't denied by Japanese spiritualists, those who can 'see' them are thought to be more vulnerable, if left untrained ('training' generally resembling Buddhist asceticism and meditation).
Now, the word 'oni' is perhaps the most overused name for spirits in Japan. This is because it can be taken to be any spirit that can and does cause harm, refer to humans whose souls have fallen into evil, and/or the legendary giant ogre-type creatures like Shuten-doji that litter Japanese legend. Because of this, it isn't uncommon for ghosts, youkai, and even some 'kami' (the animistic idea of gods in the Shinto faith) to be considered 'oni'. This should give you an idea of how useless any attempt to define what an oni is can be, and why it is so conveniently used in VNs, anime, and manga.
A lot of this lack of discrimination comes from the fact that Shinto attributes souls to all things, whether they are humans, animals, natural disasters, or even inanimate objects.
Now, the two attitudes 'traditional' people in Japan take toward ghosts tend to be: 'seal them up' or 'banish them'. While Shinto can be said to be nature-worshiping, it is at its heart a pragmatist's faith. 'Cleanse people's souls so they don't do bad things'. 'Cleanse a place to prevent possible disaster'. 'Worship a god so it doesn't squish you'. Simple, isn't it? Of course, there are a lot of deeper details, but that is what you should keep in mind as a core reality of the faith and its view on spiritualism.
In otaku-media, it is extremely rare for fantasy anime that deal with ghosts, spirits, or demons to take a single-faith approach to it. You'll almost always see a multi-faith approach, with one or more being dominant (including Christian ones at times). Shinto is dominant the most often, though Buddhism tends to dominate when you get into stuff based a few centuries in the past. Onmyoudou, one of the original types of 'spiritualism' in Japan is very much a fusion of Buddhist and Shinto ideas, if you want an example, since it is extensively used in various anime.
What does this all come down to? Basically, traditional Japanese viewpoints on ghosts and spirits tend to be ones of rejection, and this is something to keep in mind when reading a VN or watching an anime that deals with ghosts, youkai, or other supernatural beings.
A few bits of vocab:
kami- While it is a term that is also used for the Christian god, it is a universal term for all supernatural beings that have worshipers or need to be be/have been worshiped. By Japanese standards, angels and demons would be considered to be kami under the right circumstances, as the Japanese consider 'enshrining' a harmful existence to be a way to keep it from harming them.
akuma- Simply, demon. This is a relatively modern term made of the kanji for evil and the kanji for 'that which is outside/heretical'.
oni- both a name for a specific type of ogre-type youkai and a generalized umbrella term for evil spirits, humans who have fallen into evil ways to an extreme degree, and aspects of certain kami.
youkai- spirits of Japanese legend. The most common are nature spirits, animal spirits, dragons, and 'object spirits' (Tsukumogami). It isn't uncommon for beneficial or powerful ones to be raised up as 'kami' and enshrined to gain the benefit of their blessing and prevent them from doing harm. Whether they are seen as having physical form varies based upon the individual viewpoint.
Reibaishi- An almost identical concept to the Western 'medium'... basically someone who can see spirits and/or communicate with them and makes a living off of it.
Jorei- Exorcism, though it is usually of spirits rather than demons.
PS: This isn't complete... I'll be adding to it later, lol.
So I just spent 50 minutes of my day watching this. Trying to process what I just watched is hard, there's just so much information to take in. I watched it alongside OriginalRen, SuikaShoujo and The Major, yet despite our best efforts, our brains simply were no match for the depth and intricacy this anime provides.
I'll try to give you a feel, a small sample of what it feels like to watch "Issho ni Sleeping: Sleeping with Hinako", but I truly believe that the only real way to appreciate this show is to just watch it yourself.
So first off we have our heroine Hinako. Hinako really likes to sleep. Her main trait as a character is not being able to fix the strap on her shirt.
As you can see from this cleverly crafted angle, this entire anime is told in first person perspective. But we're just scratching the surface of how thick the plot really gets.
After Hinako changes clothes, covering your face so you don't see her changing, even though she just ends up sleeping in her underwear anyway, she goes to sleep.
And thus, our sleep adventure begins!
That is the face of pure bliss.
Here we have some amazing shots that truly depict the wonders of a 2D girl sleeping.
A real good close up of the heroine, it's almost like she's breathing on you
In this shot here, you can see Hinako's breasts changing sizes, giving us a clear reason why Hinako just can not get the left strap of her shirt to stay in place, her left breast simply doesn't have as much mass.
This shot here is a classic. The subtle twitch Hinako's leg makes each time really provides livelyness to her sleep, making you feel like you're sleeping right next to her.
10 minutes in and the anime really ramps it up by having Hinako turn to the other side. In my opinion this was one of their best moves yet.
Here we get a first glimpse of Hinako's windowsill which displays a clock and a vase with a plant. This is a very intringuing as the clock displays no numbers, a fact that will become really important later on so make sure you keep it in mind.
Another very rare shot of Hinako's armpit, one of my personal favorites if I daresay so myself. The disproportionally sized breasts really help elevate that armpit.
18 minutes in and the biggest game changer yet, Hinako makes use of one of her pillows! We can neither confirm nor deny if there's any significance behind this pose and the pillow's peculiar shape.
And just 30 seconds later we are shown Hinako's sleep eating abilities.
This is one of the rarest shots in the whole story, at the 22:22 minute mark, Hinako dangles her arm from the bed. What a delightful display of character.
And this 24 minute mark is the crucial turning point where we have a clear view of Hinako's room and lo and behold, nobody is sleeping next side her, even though we're supposed to be there, what could this possibly mean!?
At the 26 minute mark, Hinako has a dream about the moment we confessed to her and she gladly accepted our feelings. While the dream itself lasted a mere 10 seconds, I could really feel a deep emotional connection with Hinako's character just from watching her sleep for the past 26 minutes.
And in the next minute, Hinako wakes up. I'm sure we were thinking the same thing, and that is how much we love each other. Hinako, being the amazing girlfriend she is, sings us a lullaby with really inspiring lyrics such as "Go to sleep, go to sleep on Hinako's chest" which have the result of making her fall asleep.
At the 30 minute mark, Hinako has yet another dream, this time about when she was training hard to lose weight, she even gives us advice on how to be BIG like Hinako.
And now, the biggest game changer yet, Hinako falls off her bed! My heart could barely take it, seeing Hinako fall on the floor after 30 minutes of sleeping really came out of nowhere, this anime sure knows how to tug on your heart strings.
And now starts the most romantic scene in an anime I have ever seen.
What a straightforward approach. Hinako tops all those tsunderes in generic romcoms, you don't get this level of romance too often.
Of course we have a really deep connection with Hinako, and she reassures us of that by returning our feelings (even though we didn't really say anything, I'm sure our feelings got acress).
I had to hold back my emotions over how realistic everything got, the intense urge to kiss my screen really started to come out.
Hinako wastes no time though, she knows what her main goal is, this woman has her priorities set straights, that's why right after this she once again heads to bed and instantly falls asleep. Pro sleepers really are something else.
But the thrilling ride isn't over yet, can you believe they still have more in store? This time, Hinako invites us to sleep on the same bed as her. My heart almost jumped out of my chest. The anime really makes this a realistic experience by tilting the camera 90 degrees. It truly felt like I was right next to Hinako.
35 minutes in, Hinako does yet another unpredictable thing, she decides to get a night snack. Gosh, this anime really doesn't hold back on the plot twists.
Brushing your teeth is important too. Even if you didn't eat anything. Deep.
Once again, after falling asleep, Hinako falls on the floor. This time facing the other way, I liked that change of pace, this anime really knows when to spice it up.
She doesn't forget her girlfriend duties though and reminds us we are also an entity, a sentient being, and thus we need sleep as well. Notice how her strap keeps sagging lower and lower, symbolizing we're reaching the end of our journey.
After she falls asleep, Hinako has one last dream. In this one though, she ended up getting fat due to eating so many snacks. I'm sure she'll resume her training the next day!
And now, after a whole 40 minutes of Hinako sleeping, morning comes, and this is where the plot really thickens!
You see, after this, Hinako sleeps with us again, twice, do you not see what this means!?
This whole time, we've actually been trapped in a dream world, but not just that, we were trapped in a dream world, inside a dream world, inside a dream world, inside a dream world, and we weren't a human being either, we were a ghost that posessed random objects around Hinako's room in order to try to wake her from the dream by looking at her body from several different angles. Remember the clock I mentioned at the beginning? What was missing? Pointers! That's because in this dream world, there's no time flow! We've been stuck sleeping with Hinako over and over, that's why she always wears the same outfit when she sleeps.
I could barely see this coming, it came by so fast my brain just had no time to process it.
This anime is a deconstruction of the human psyche, one that if you're not paying attention to, you will miss its profound message, the 50 minute length time really manages to portray to intricacies of the brain by having the same still shots over and over again across the timeline, you really feel like you're diving into Hinaki's profound sleepiness and tracing its patterns.
The emotional bonds you manage to form with Hinako as you watch her sleep from every possible angle really make this a standout from the crowd. You can not get this deep level of characterization anywhere else.
It brought me to tears as my eyes were strained while I wtched 50 minutes of a girl sleeping on a bed, making me empathize with her.
The story sucks you in, almost making you fall asleep just like Hinako.
This 16 year old girl who can't put on a shirt strap properly is the apogee of all female characters. If you haven't used the term "waifu" now, I'm sure this anime will change your mind.
Issho ni Sleeping: Sleeping with Hinako is, without a doubt, the best anime ever made.