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Manga / Summer Time Rendering

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Duetagonists posing

"Don't forget to find me."
Ushio Kofune

Summer Time Rendering (サマータイムレンダ in Japanese) is a shonen manga by Yasuki Tanaka. It was serialized online in Shonen Jump+ from October 2017 to February 2021, and compiled into 13 volumes. An anime adaptation by OLM Incorporated was released as part of the Spring 2022 anime lineup.

Shinpei Ajiro returns to his hometown on the island of Hitogashima to attend the funeral of his childhood friend, Ushio Kofune.

She was thought to have drowned while saving a child from being swept away at sea, but it's not long before evidence surfaces that her death was no accident. Furthermore, it may have been connected to the "Shadow Sickness", a local legend regarding mysterious entities that can steal your identity, murder you, and take your place. It all sounds like a bad joke to Shinpei — until Ushio's sister is held at gunpoint by a clone of herself, right before his very eyes. It puts a bullet in her head, then turns the gun on him and pulls the trigger.

Shinpei immediately wakes up in a cold sweat while on the ferry headed to his hometown on the island of Hitogashima, on his way to attend the funeral of his childhood friend, Ushio Kofune.

The story starts off as a supernatural mystery where the cast unravels the truth behind Ushio's death and learns the hard way who can and cannot be trusted. As the true nature of the threat lurking the island is revealed, the stakes ramp up until the story evolves into a fast paced, Action Horror thriller that requires our heroes to employ more drastic measures in order to outwit the enemy and stay alive.

The series has a short Spin-Off manga, Summertime Rendering 2026: The Room that Dreams of Murder, focused on Nagumo/Hizuru and her niece as they happen upon a haunted apartment. The Light Novel Summertime Rendering 2026: Nagumo Ryuunosuke's 100 Views is a direct continuation which follows the two of them as they solve supernatural mysteries around Tokyo.

A visual novel adaptation of the main series, Summer Time Rendering: Another Horizon, was released in Japan on January 2023 for the PlayStation 4 and Nintendo Switch.

Summer Time Rendering contains examples of:

  • 11th-Hour Ranger: Near the end of the series, Shadow Ushio is finally able to summon from within herself the good version of Haine that Hizuru befriended in her youth. She joins Shadow Ushio and Shinpei in the final fight against Shide in Tokoyo the Eternal World.
  • Abandoned Hospital: The old abandoned clinic owned by Sou's dad is a suspicious, run down building where several plot important events take place. Hizuru first met Haine here 14 years ago, Ushio and her shadow encountered a stray shadow here two days before her death, and Shinpei, Sou, and Shadow Ushio discover an entrance to a locked secret passageway behind a creepy headless statue in the operating room.
  • Action Girl: When facing off against the shadows, most of the female cast can hold their own in a scrap thanks to their own shadow related abilities. Shadow Ushio and Shadow Mio utilize their natural super speed and strength in every skirmish, Hizuru can see two seconds into the future by letting Ryuunosuke take control of her body, and while Tokiko cannot fight directly, she makes full use of her two massive shadow bodyguards in the midst of combat.
  • Adaptation Distillation: Several minor subplots and expository details had to be trimmed down so that the 13 volume story could fit into 25 episodes.
    • Tokiko's alliance with Shide and Haine is revealed and discussed between Shadow Ushio and Shinpei long before they meet in Hiruko cave, and when Shadow Ushio shares her memories of the previous loops with everyone Sou and Mio confront her for her treachery but end up forgiving her. None of this was shown in the anime.
    • In the fourth loop, Nezu had captured the shadow that killed and copied his wife but can't bring himself to kill her off no matter how hard he tries. The anime skips this entire scene, so she doesn't appear until the second half of the story when Nezu finally finds the resolve to finish her off.
  • Adaptation Expansion: The final episode adds more meat to the manga's epilogue by including multiple scenes featuring various characters and their lives in a timeline free from the shadows' influence, as well as expanding on the reconciliation between Shinpei and Ushio after they had refused to talk to each other for two whole years.
  • Affectionate Nickname: Both Mio and Shadow Mio refer to Shinpei by "Shin-chan".
  • All There in the Manual: Several extra chapter records contain in-depth information regarding the finer details of how the shadow mechanics work. Most are based off observations made by Shadow Ushio, Shinpei, and Hizuru, while Shadow Mio's Extra Chapter is a major extension of the post-school battle interview that didn't make it into the main story.
  • Amnesiac Resonance: In the Shadow-free world, Shinpei and Ushio both dream of the previous world with Shinpei remembering Hizuru Minakata and her identity as Ryuunosuke Nagumo along with other bits and pieces such as finding Haine Minkata very familiar. It's hinted that Shinpei and Ushio regain their memories at the festival, as they both remember the promise at the old clinic in the previous timeline.
  • The Atoner: Both Tokiko and Dr. Hishigata sided with Shide thinking they were protecting their loved ones. After they each learn what Shide's real goal is and that he'll betray them once they've outlived their usefulness, they resolve to make things right by doing everything in their power to help fight against the shadows.
  • Beach Episode: A rather serious beach episode occurs within a short but laid back trip to the beach.
    • Shinpei takes Sou to an empty beach so he can entrust him with his secrets regarding what he's seen in his time loops and reveal that Ushio lives on through her Shadow. Hijinks ensue when Sou reacts to Shadow Ushio like he's seen a ghost.
    • After using her cell phone to regain her memories, Shadow Ushio uses her power to show Shinpei and Sou her memory of the day Ushio died. It starts with everyone in their swimsuits having a fun day at the beach, but it's not long before Shiori is dragged into the water by her shadow while nobody is looking and Ushio's rescue attempt ends in failure.
  • Big Bad: Hiruko is the progenitor of all shadows on the island and her existence is ultimately responsible for every shadow related misfortune that occurs in the story. Shidehiko takes her place in this role once his intention to use the power of her eye to destroy the world is revealed.
  • Book Ends: The story begins with Shinpei returning to Hitogashima to attend Ushio's funeral. The final chapter has Shinpei returning to the island to see Ushio, who is now alive, again.
  • Cassandra Truth: Defied. Aware that looping back to the past after a clone of Mio killed him twice is an outlandish claim, Shinpei avoids being labeled a crazy person by filming evidence of Shadow Mio and using it to successfully warn Mio and Sou about the existence of the shadows. He decides to leave out the time travel part until later loops when he has Shadow Ushio to back up his claims.
  • Central Theme: What is the difference between the original and a perfect copy?
  • Chekhov's Armoury: Some of the most effective tools in the war against the shadows (as well as a few nasty surprises from Haine's side) are the slew of innocuous items and details that wind up having great importance later on, all of which can be easily missed by viewers the first time around.
    • When Mio and her bike flip over and tumble into the ocean at the beginning of the story, Shinpei sees her striped underwear. A few loops later, the scene helps him realize that he can't stop Shadow Mio's creation because Shadow Mio's underwear (which he also caught a glimpse of when she stabbed him to death) was white, Mio said she last changed her underwear from white to stripes on the 21st, and he can only loop as far back as the morning of the 22nd.
    • During the third loop, Shadow Shinpei grabs Shinpei's cell phone and erases it for no discernible reason. It isn't until much later that we learn that shadow copies of devices that run on electricity only become fully functional if the original is erased. In the eighth loop, the shadows Haine absorbed and brought with her from the third loop allow her to not only transform into Shadow Shinpei but also have a functional copy of his cell phone at her disposal even though the original cell phone still exists in this timeline. She then proceeds to use his voice and the phone to trick the cast into splitting up so that Shide can have an easier time picking them off.
    • Sou finds a bottle of mercuric chloride while investigating the abandoned clinic, noting that it was used to treat syphilis before it was discovered to be extremely toxic. Shinpei secretly pockets the bottle and ends up ingesting its contents as a last resort method to escape the fourth loop via suicide.
    • In the same clinic, Shadow Ushio finds a very old photo album belonging to the Hishigata family. It's later revealed that someone who strongly resembles Karakiri is standing in one of the photos, providing further proof that he is Shide's true identity.
    • Shadow Ushio demands to be bought takoyaki at the festival in exchange for using her powers to slip inside a crack in the abandoned clinic's wall, and Shinpei promises to buy her 10 or 100 pieces. Ushio and Shinpei remembering this exact conversation is the trigger that causes their memories of the entire adventure to come flooding back to them at the very end of the story.
    • While exploring Hiruko Cave, Shinpei deduces from the abundance of sea water present that an escape route that leads out into the ocean has to exist. He ends up utilizing it in the ninth loop as part of his plan to retrieve that timeline's version of Shadow Ushio and launch a swift assault on Haine's main body.
    • In the fifth loop, Shadow Ushio tries to convert Nezu's two nail guns into shadow copies in order to supply them with infinite ammo, but because her memory banks are full she can only convert one of them. The normal nail gun becomes the key to taking down Haine in the final loop's cave battle. She falls for an ambush because she is unable to sense the presence of either the nail gun or its wielder Sou, since neither of them are made of shadows.
    • The mud that makes up Shide's armor is able to completely hide the wearer's presence, so when Shadow Ushio tries to reveal his true identity in the fifth loop her scan turns up blank. Realizing that something similar might work on the tracking brand on his arm, Shinpei is able to keep his location from Haine a secret in the ninth loop by hiding inside one of Tokiko's stray shadow minions.
    • Shadow Ushio suggests trying to stop the festival by stealing all the fireworks and using them to blow up the festival grounds. That plan is shot down because it would achieve nothing but cause mass panic among the civilians. Guess what Shinpei uses to destroy the massive shadow barrier that was erected to protect Hiruko's inner sanctum in the final loop.
    • Mio collects several strands of the original Ushio's hair for Shadow Ushio so she can use its data to restore some of the damage done to her body. When Shide inflicts massive damage on Shadow Ushio during the final battle, she reveals that she still has several of the strands left and uses them to regenerate enough of herself to deal a decisive blow to Hiruko.
  • Chekhov's Gift: Ushio visited Shinpei in the first chapter (July 22nd) and gave him Haine's eye, starting the time loop.
  • Closed Circle: The setting is an island 4km away from the mainland, with only a ferry responsible for bringing and returning people from the island. As Hizuru notices, the boat operatives are already Shadows themselves, and considering that now the Shadows know they have opponents, if any of the heroes try to leave, they're likely to be killed on the trip.
  • Closet Gay: It is strongly implied that Tokiko has feelings for her best friend Mio, but she is never able to muster up the courage to tell her directly because she knows that she is in love with Shinpei. The rest of the cast is unaware of this since she keeps those feelings to herself.
  • Cowardly Lion: Totsumura is just about the textbook definition of this. While normally cynical and cowardly, when push comes to shove, he's able to step up.
  • Curb-Stomp Battle: Haine's guardian, Shide, is a towering humanoid shadow monster that cannot be killed by conventional means, so most encounters with this walking nightmare end with his opposition on the verge of death or turned into a corpse within a matter of seconds.
    • Poor Hizuru receives the brunt of Shide's beatdowns in almost every loop where she dies. The summer festival? He reflects her gunshot back at her, leaving her unable to stand. Hiruko cave? He fatally wounds her with a well aimed pistol shot after a brief shootout. Koba Mart Round 2? Guess who's there, ready to chuck her out the window and smash her head into the pavement. Torajima Beach? She puts up a good fight this time, but thanks to an ill placed time loop Shide gets a do-over and easily emerges victorious.
    • Shinpei, a regular human with no noteworthy combat abilities, usually cuts straight to "curb stomped" status the moment Shide enters the scene. But during the gymnasium showdown, he and Shadow Ushio finally dish out a one-sided victory against Shide and Haine by using a carefully coordinated gas explosion, some clever shadow maneuvers from Shadow Ushio, and a bulletproof vest Shinpei slapped together ahead of time for good measure.
  • Dark Is Not Evil: Ushio who, despite being a shadow, is firmly on the side of the heroes and is the series' co-protagonist.
  • A Day in the Limelight: The start of the fourth loop follows Hizuru's point of view on the morning of July 22nd and spends a good amount of time revealing what she was up to during Ushio's funeral. Thanks to her prior experience with shadows, she too suspects that Ushio's death was no accident and is able to come up with a plan to eliminate Shadow Alan before it can murder Alan.
  • Dead Person Conversation: The story begins with Shinpei talking to Ushio in a dream. He's headed to her funeral.
  • Disguised Horror Story: The promotional materials for the anime, the cover of the first volume, and the prologue suggest a coming of age story with a hint of romance and intrigue on a sunny, rural island. While things take a sudden turn for the worse when three characters are murdered in cold blood by the end of the first chapter, the plot doesn't show its true colors as a horror thriller until the corpses pile up at the summer festival.
  • Earn Your Happy Ending: Shinpei goes through multiple loops and deaths before he's able to erase Hiruko, and ultimately prevent all the events of the story from ever happening, including preventing Ushio's death.
  • Eldritch Location: Haine's home world exists in an alternate dimension outside of time where only shadows can safely reside, whereas humans who step foot here will slowly break down and turn into dust. The space is presided over by a red sky and a permanent black sun, and the contents of the dimension are determined by Haine's memories and current mental state.
  • Everybody Lives: In the ending, a new world where Shadows never existed is born, which saves all major characters from their deaths, including Ushio, Shinpei's Parents and Ryuunosuke, who are alive and well in the present time. Haine is also re-incarnated into Ryuunosuke's young daughter and a good friend to Shiori. Shidehiko, no longer being a shadow, is implied to have lived and died like a normal person, with his descendants still watching over the temple.
  • Evil Doppelgänger: A shadow has the power to turn into a perfect clone of a human right down to their DNA, memories, feelings, and personality. But when it isn't busy impersonating the original, a shadow will tend to have a more cynical and resentful personality reflecting any negative emotions the original may have been suppressing. These shadows are also ruthless, borderline sadistic killers who show no remorse towards harming anyone who gets in between them and their targets, including friends and loved ones their original would give their lives for.
  • Extremely Short Timespan: The manga takes place between the 22nd and 24th of July, in the span of these 3 days a lot of stuff happens, granted, that days repeat due to the time loop. The night of 22nd in particular takes place over the course of roughly 20 chapters, which Shinpei lampshades to be a night that seemed to never end.
  • Flash Sideways: During the festival on July 24th, Shinpei is the only one who notices Ushio walking through the crowd in a pink yukata despite the fact that she should be dead. He chases after her, only to instead run into her shadow dressed in the swimsuit she died in. What he had caught a glimpse of was a vision of the real Ushio from an alternate timeline where she never died because shadows do not exist there.
  • Foreshadowing:
    • First two hints that Shinpei's heterochromia isn't natural: Ushio's unknown gift at the start of the story glitches out his vision when she gives it to him, and the family photo at the funeral shows him as a child with two dark blue eyes.
    • One of the last things Ushio tells Shinpei in his dream on the ferry is "Don't forget to find me". He ends up searching for her Shadow on the beach during the summer festival, and again in the second to last loop when he has to scour the sea for the current timeline's iteration of Shadow Ushio before Haine's shadow army destroys her.
    • Amidst the carnage at the summer festival, Tokiko says "this isn't what I dirtied my hands for!" before Shide kills her by stabbing her in the head. In the next loop we learn that she's been working for Haine and Shide, and both plan to eventually betray her.
    • The ritual at the end of the summer festival cuts to a scene of a melting shadow in a wheelchair next to Dr. Hishigata and another of Nezu at his house aiming his rifle at something. Both of them are eventually revealed to have wives who were turned into shadows.
    • Shide makes crypic comments during the ritual, such as wanting to "cut the power" to this world and proclaiming "This is my ending". His true identity is a huge fan of video games and his true goal is to usurp Haine's ritual so he can completely destroy reality.
    • Several clues point towards Shadow Ushio's true identity as Haine's counterpart, such as time traveling alongside Shinpei at the same time Haine does at the end of Loop 3, feeling deja vu at the abandoned clinic where Haine used to live, and obtaining the unique ability to hack other shadows just like Haine can. A more subtle hint is that Shinpei's mismatched eye is light blue like Shadow Ushio's eyes rather than blood red like Haine's eyes, hinting at their connection.
  • Funetik Aksent: Most of the main cast and the townsfolk talk in the Kansai (Wakayama-ben) regional accent. This is localized in the English translation of the manga to a phonetic drawl that brings to mind Steinbeck's dialect style at times.
    Totsumura: Whassa matter, Mio-chan? Watcha staring at yer own house for?
  • Grandfather Paradox: Shadow Ushio is transported back to the past where she erases the whale form of Hiruko before it could copy and devour Haine. This causes Ryuunosuke, Hiruko, Haine, and eventually Shadow Ushio to disappear since they were all created from shadows that no longer exist. Meaning there is now nobody capable of going back in time to erase the whale in the first place, thus creating the paradox.
  • "Groundhog Day" Loop: A variant. Each time Shinpei dies, his start point moves forward by a certain amount of time, ranging from a couple of minutes for the first few loops to several hours for the later ones. This means that anything that occurred before the start of each new loop, such as sustained injuries or the deaths of anyone aside from him, will be rendered irreversible.
  • Guys Smash, Girls Shoot: Inverted.
    • Shadows are much stronger and faster than humans, but Shadow Ushio, Hizuru, and later Tokiko and Shadow Mio all have the means to move into close quarters and engage them with their fists, sledgehammers, or knives. Mio, the only outlier, uses Sou's aerosol flamethrower in the one fight she's involved in.
    • Shinpei, Sou, Nezu, and Totsumura are all humans who need to keep a distance from the shadows for their own safety, so they typically fend off the shadows with ranged weapons such as modded nail guns, makeshift incendiary weapons, and firearms. Even after inheriting Ryuunosuke's abilities from Hizuru, Shinpei opts to hang back and provide covering fire until the final battle, where he takes up the sledgehammer after his shotgun fails to hold Shide back.
  • Heel–Face Turn: Tokiko joins the heroes' side on the seventh loop after she learns the truth about what the shadows will do to both her family and Mio. Shadow Mio also allies with them after Ushio cuts her off from Haine's influence in the aftermath of the gym battle.
  • Homage: Several elements of the story pay homage to the Siren Games, a series of early 2000s survival horror games.
    • The setting is similar to that of Siren 2, which takes place on an island where an entity called Mother tries to escape her underground imprisonment using her army of Yamibito.
    • The shadows' ability to sense each other's presence resembles a core mechanic of the Siren series called "Sightjacking", a skill that allows the protagonists to psychically see through the eyes of the Shibito which they obtained as a side effect of slowly turning into Shibito themselves.
    • Hiruko first appeared as a whale that washed up on shore, copied and devoured the first girl who approached her, and was revered as a deity after turning several other islanders into shadows to save them from a famine. This is a toned down version of the origin of the first game's Datatsushi, an alien that crash landed near a starving village. The villagers mistook it for a fish and ate it alive, so in retaliation it used its dying breath to curse all but one of them to death. The lone survivor was bestowed immortality and started a religion based around bringing Datatsushi back to life.
    • Tokoyo, the setting of the final battle, is a nod to the Yamibito Dimension from Siren 2. Both are alternate realities with a red sky, perpetually eclipsed sun, and populated with docile shadows/Yamibito.
    • The final battle itself mirrors the climax of the first Siren game, where Shinpei/Kyoya chases the weakened final boss into an alternate dimension with no way of returning and finally destroys him with the one weapon Shide/Datatsushi is vulnerable to.
    • The author confirmed that the volume extras were inspired by the documents and snippets that can be collected in the games' Archive system.
  • In Spite of a Nail: In the Shadow-free world quite a few things remain the same.
    • Shinpei still returns to Hitogashima two years after he left thanks to Ushio, but because of her call rather than her funeral.
    • Shinpei's friendships with Ushio, Mio, Sou, and Tokiko carry over and Sou still has a crush on Mio.
    • Hizuru Minakata is still a successful author under the pen name "Ryuunosuke Nagumo" and she still returns to the island on the same ferry as Shinpei but this time to celebrate her niece's birthday.
    • The Karikiris are still the local Shrine priests, but are entirely normal with the elderly Iwao Karikiri simply having a Strong Family Resemblence to his ancestor.
  • It Only Works Once: Once Haine starts retaining her memories of the previous loops, not a single plan attempted by the heroes works a second time.
    • Shinpei, Hizuru, and Nezu raid Shadow Shiori's house like they did in the previous loop, this time to have Shadow Ushio erase her once and for all. Unlike last time, Haine knows they're coming and has Shide lie in wait for them, aiming to capture Shinpei alive to prevent him from looping. Hizuru and Nezu end up dead, forcing Shadow Ushio to decapitate Shinpei which activates his looping power in the nick of time.
    • During the battle at Torajima, Hizuru peels Shide's armor off by having Ryuunosuke invade his body, but the fight and its conclusion are erased from reality thanks to Shinpei activating the loop elsewhere on the island. Only Haine and Shide retain their memories of the fight, so when Shinpei and Ryuunosuke come up with and attempt the same tactic in the final battle, Shide already has the know-how to counter their trick.
  • I Should Write a Book About This: In the Shadow free world, Hizuru is inspired by Shinpei's dream to start writing a new book entitled "Summer Time Rendering".
  • I Want My Beloved to Be Happy: Tokiko fully supports and encourages Mio in her attempts to tell Shinpei her feelings despite being in love with Mio herself. While consoling Mio after Shinpei rejects her confession, Tokiko compliments her for being brave enough for going through with it, adding that she wouldn't have been able to say a thing.
  • Kill and Replace: The life cycle of a shadow is as follows: Copy a human, kill and consume them within seven days, live out the human's entire life like nothing happened, pretend to "die" with the assistance of the Hishigata Clinic, find a new target, rinse and repeat.
  • Last Stand: Nezu and Tokiko both do this in the final loop by staying behind to hold one of Shide's bodies off so the rest of the crew can make a break for Hiruko's lair. They manage to survive, however.
  • Legacy Character: In a sense. Ushio died before the start of the series and the Ushio we follow for 99% of it is her Shadow.
  • Like an Old Married Couple: Despite being obviously in love with each other and having each other's best interests at heart, Shinpei and Ushio (and by extension her Shadow) bicker with each other constantly, with most of their arguments starting when Shinpei scolds her for charging head first into situations without thinking or Ushio hurls insults at him for being stubborn and overbearing with her. Shiori's friends get a kick out of their petty squabbles and make sure to tease them by calling them a married couple at every chance they get.
  • Living Shadow: The 2D shadow cast beneath a clone's feet is the shadow's true body, and it will move out of the way independently of its clone if anyone tries to step on it. While injuries sustained by the clone body can be healed in a matter of seconds, any damage done to the shadow itself is irreversible, including fatal damage.
  • Masquerade: To the residents of the island, shadowy clones murdering you and taking your place is nothing more than a local myth called the "Shadow Sickness". The Hishigata Clinic has been enforcing this secret for generations by fabricating the victims' causes of death, diagnosing witnesses with Capgras Syndrome, and disposing of people who try to poke their noses in too deep.
  • Maybe Ever After: Sou and Mio in the new world, as she doesn't reject his confession outright instead asking what he likes about her.
  • Meaningful Echo: During a pause in their scuffle, Shadow Mio demands to know why Shadow Ushio is protecting Shinpei, a human who had a hand in killing one of their own a few hours earlier. Shadow Ushio yells, "I love Shinpei. What's wrong with siding with the person ya love?!" In the final loop, Shadow Ushio begs Shinpei not to follow her into Tokoyo, a dimension that humans can never return from. He refuses, stating "I love ya, Ushio. And I want to be with ya. Got a problem with that?"
  • Meaningful Name:
    • Ushio's name is spelled with the kanji for "tide" (潮). After falling unconscious when her memories were erased by Shadow Shiori, her Shadow drifted along with the ocean currents until the high tide washes her up on the beach on the night of July 24th.
    • The four armed shadow, Shide. As Hizuru mentions, it is written in a similar way to "4 arms" ("Shi" is a pronunciation for the kanji for four, 四; "de" is a pronunciation for the kanji for arm, 手). Shide's name also gives a clue as to his true identity, as 'shide' are a type of paper streamer that are commonly used as a tool for Shinto rituals, indicating Shide's true identity as Shidehiko Hishigata/Masahito Karikiri.
  • Missing Mom: Ushio and Mio's mother died shortly after the latter was born, meaning that Alain raised them (and later Shinpei) as a single parent for most of their lives.
  • Never Got to Say Goodbye: Shinpei left the island to attend a cooking school in Tokyo, but he and Ushio never bade each other goodbye due to a heated argument they had with each other earlier that year. Both of them come to deeply regret it, as Ushio spent her final moments wanting to see him one last time while Shinpei lives with the fact that he never set things right before her passing. In the timeline where the shadows don't exist, Ushio doesn't die, so Shinpei is able to see her again and finally make amends with her.
  • No Communities Were Harmed: The story takes place on the island of Hitogashima off the coast of Wakayama City, Wakayama Prefecture. The setting is a stand-in for the real life uninhabited island of Tomogashima, and various locales such as Koba Mart, the ferry dock, and many other backgrounds can be found on the mainland town of Kada and the tiny island town of Ogijima.
  • No Ontological Inertia:
    • Any object created by a shadow will cease to exist if its creator either dies or moves at least 50 meters away from it. This does not seem to apply to any "children" spawned by a shadow.
    • Haine is the mother of every single shadow on the island. If she is ever fully destroyed, all the shadows will disappear along with her.
  • Ominous Visual Glitch: Thought your picture was still loading in? Nope, both the manga and the anime have pixelated graphical glitches in many scenes taken directly from Shinpei's perspective. It's soon revealed that this effect is synonymous with the shadows, and it's visible to anyone who manages to spot one in the middle of transforming.
  • Once More, with Clarity: The first chapter opens with Shinpei dreaming of Ushio, who gives him a gift before telling him to protect Mio. The second-to-last chapter reveals this was actually the future shadow Ushio invoking a Stable Time Loop by giving Shinpei Haine's eye, the item needed for Shinpei to be able to erase Hiruko before she ultimately disappears.
  • Panty Shot: A plot-relevant case, where Mio's bike crash to meet Shinpei in the docks ends up giving the latter a full view before she hits the water. When he gets thrown into his first loop and thinks he's simply suffering a bad nightmare and some Déjà Vu, it's seeing this exact scene with the exact same panties that gives him one of the major clues to what's really happened. It also becomes relevant not long thereafter because the Mio shadow that's trying to kill them is wearing white, whereas the docks scene established the real one's wearing stripes that day.
  • Parental Abandonment: Shinpei's parents died in an accident, which was why he was adopted into Ushio's family. In reality, they were killed by Shide when they discovered the shadows during a dive. Shinpei erasing Hiruko in the past retroactively prevents their deaths as well as they are alive in the epilogue.
  • Person of Holding: Shadows can carry several objects within themselves by storing the data in their brains and generating a copy of the object whenever it is needed. Shadow Ushio uses this power to store things like weapons, an extra change of clothing, and items that may or may not be relevant later on in the story, while Shadow Mio carries her knife and at one point several giant crates full of fireworks.
  • Photographic Memory:
    • Almost literally in the case of the shadows. After scanning a human with a flash of light that sounds like a camera going off, a shadow will gain a perfect working memory of every single detail of that person's life.
    • Though shadows no longer exist in the new timeline, the now teenage reborn Haine has an eidetic memory. She demonstrates this ability in the sequel by memorizing a screen full of numbers that flash across a TV for only a few seconds.
  • Public Secret Message: In order to keep her whereabouts and identity a secret from the shadows, Hizuru encrypts her contact info with a code that can only be deciphered using her real name and her pen name. At that point in time only she and Nezu know that she has a pen name, so by Hizuru's logic the only other person who could crack the code should be the time traveler she is searching for.
  • Race Against the Clock: At 9:00 pm on July 24th, the shadows will invoke a mass murder ritual that consumes every single human on the island. Shinpei only has three days and a limited number of retries to figure out who or what is behind this scheme and how to stop them.
  • Reincarnation: In the new timeline at the end of the series, Haine is reborn as Ryuunosuke's daughter. She has no memories from her time as Hiruko's vessel, but she retains her "copy" ability in the form of eidetic memory.
  • Required Secondary Powers: Ryunosuke can grant his host the Super-Strength of a shadow but not any Super-Toughness, and even relatively limited use of this power can cause serious injuries.
  • Shout-Out:
    • Shadow Ushio dons a mask with pink hair and a heart tiara, spins around, and calls herself a Cure before her charade is cut off. Nezu later asks if she's a Pretty Cure girl after witnessing her fight and transform like a magical girl.
    • The cipher needed to decrypt Hizuru's contact info is described by Shinpei as an unsolvable code that appeared in " The Tamam Shud Case" from one of her novels. This was based on the real life mystery of the Somerton Man, a death that went unsolved until 2022 involving an unidentified body, a scrap of paper with the words "Tamam Shud" printed on it, and a cipher (used verbatim in the manga) found in the book the scrap of paper came from.
    • The stray shadow guardians Rosencrantz and Guildenstern are named after two famous characters from Hamlet. Both sets of characters end up betraying Haine and Hamlet respectively.
    • Masahito discusses his love for JRPGs with Shinpei, in particular Final Fantasy VII and its upcoming remake. Winds up being thematically relevant immediately afterwards when it's revealed that Hiruko and Shide are very similar to JENOVA and Sephiroth in origin and motivation respectively as well as the fact that Shadow Ushio is killed by Shide in a very similar manner to Aerith.
  • Stable Time Loop: In the penultimate chapter, Ushio goes back in time before she disappears as a consequence of erasing Hiruko to give Shinpei Haine's eye to give Shinpei the means to reach the conclusion needed to end the loops and as well as leaving Hizuru the message so she would come to the island.
  • The Strategist: Both Shinpei and Nagumo are sci-fi thriller novel enthusiasts who make full use of their wits and knowledge of the genre to outmaneuver their enemies. Their ability to use their limited time, resources, and allies to come up with effective countermeasures against the shadows, prepare accordingly, and adjust their plans on the fly enables the rest of the cast to stand up against supernatural foes several times stronger than them.
  • Summon Magic: Tokiko fights by summoning two giant wild shadows named Ros and Guil that obey her commands.
  • Teleportation Rescue: Each time Shinpei dies only his consciousness will return to the past, but Shadow Ushio will physically follow him back in time as long as she wasn't killed in the previous loop. In order to escape their captors Shide and Haine in the fourth loop, Shinpei drinks an entire bottle of poison, grabs ahold of Shadow Ushio with his consciousness once he finally succumbs to it, and pulls her into the time warp just in time to avoid an incoming fatal strike from Shide's blade.
  • Timey-Wimey Ball: Although the power to time travel comes from the same source, Shadow Ushio follows her own unique set of looping rules. Rather than returning by Mental Time Travel, the Shadow Ushio who appears on the beach during the summer festival physically follows Shinpei to each new timeline and materializes somewhere near him, complete with any injuries she sustained from previous loops. This means that two Shadow Ushios can exist in a single timeline, an anomaly that Shinpei eventually realizes and exploits in order to repair her destroyed body in a later loop.
  • Title Drop: "Summer Time Rendering" becomes the title of Hizuru's new novel idea, directly inspired by Shinpei and Ushio's recollections of the loops and the shadows via dreams.
  • Tomato in the Mirror: Ushio, has two. First there's the reveal that she's really Ushio's shadow which comes fairly early. The second, and far bigger one, is her slow realization that she's actually the part of Hiruko that was split off fourteen years prior.
  • The Unreveal: As a result of Shinpei traveling back to the starting point after being murdered twice, we are never shown who asked the innkeeper for the whereabouts of "the lady with the huge honkers" in the first loop. But piecing all the hints from the first three loops together will reveal that it was the Shadow Shinpei created at the funeral by Shadow Shiori.
  • The Very Definitely Final Dungeon:
    • The first part of the final fight takes place in Hiruko's Cave, a large underground cave connected to the sea, populated by Shadows, como of which take the form of sea life living outside water, with a shrine-like area where a major antagonist lays.
    • The actual final fight takes place on an alternate world where time stands still, disabling Shinpei's loop power and Ryuunosuke's future vision. The place looks like Haine's village and even reenacts the air raids she suffered in life.
  • Villainous Lineage: The Hishigata family has been serving Haine for generations, and their first member and clinic founder, Shidehiko Hishigata, was the first Shadow she created, currently acting as Shide.
  • Whole Episode Flashback: Episode 9 covers the story of the day Ushio met and befriended her shadow as well as the day that Ushio and Shiori were killed by Haine.
  • You Have Outlived Your Usefulness: Done by Shide to Tokiko in multiple loops. Realizing that this is their inevitable fate and that Shide's been lying to them is what causes both her and her father to join Shinpei.
  • You Killed My Father: Shinpei's parents were killed after they discovered the shadows during a marine research dive.