S1 E1 • Ougi Formula, Part One

Koyomi and Ougi find themselves trapped in a classroom, and the story shifts back to the point when Suruga introduces Ougi to Koyomi. Ougi approaches him with a mystery about a room not seen in the school's blueprints for them to investigate. When they enter the room, they find themselves trapped inside, leading them to their current situation. While talking about their predicament, the duo realize that the room is an oddity created by a traumatic memory from Koyomi's freshman years. Koyomi then tells Ougi that two years prior, the class president at his and Hitagi's class at the time, Sodachi Oikura, was looking for possible culprits of cheating on a math test, and would not allow any student to leave class until a culprit was found. Ougi surmises that they themselves won't be able to leave the room until the two-year-old mystery is solved.

S1 E3 • Sodachi Riddle, Part 1

Koyomi enters the classroom against Hanekawa's advice and talks to Sodachi, who has a venomous hatred for him, and he cannot believe that it comes simply from the class meeting two years ago, as she enigmatically mentions that he has no idea what makes him what he is, as he cannot remember what was in his shoe locker the first year of middle school. She winds up stabbing him in the hand with a pencil just as Hitagi comes in, although Hanekawa is tying to stop her, and the two have a fight. Later, Ougi accompanies him to his former middle school, and they go to his old shoe locker, which contains envelopes with his name on them. One of the envelopes contains a map, which leads to a dilapidated old house where Koyomi remembers that he explored regularly every summer during middle school, and where he met a girl.

S1 E4 • Sodachi Riddle, Part 2

Koyomi recounts to Ougi how he had originally found similar letters in his shoe locker when he was in his first year of middle school, and how they intrigued him. He came to the house and the girl explained how she had sent similar letters to others and how he was the only one who responded. She began helping him study maths and this helped him to become as good at it as he eventually became, and was critical to him getting into Naoetsu High School three years later. She imposed three conditions on him that they should always meet only in the house, to keep the study sessions a secret, and that he should not probe into her life. On the last day of summer vacation Koyomi went to the house as before and found it empty. He found an empty envelope taped to the bottom of their study table. He never saw the girl again. He tried looking for her at school to no avail. Ougi concludes that the mystery girl must be Sodachi, although he is perplexed at why she would not have reminded him of their former acquaintance when they later became classmates in high school. Ougi explains that the reason why Sodachi invited him over for their study sessions was because her family was experiencing domestic violence and that she knew that Koyomi's parents were police officers, and she hoped he and his parents might be able to help her family. His middle school self, however, was not able to understand this and her family eventually fell apart completely by the end of that summer. The next day he shares Ougi's conclusions with Hanekawa, who points out Ougi's conclusion hinges Sodachi knowing that Koyomi's parents were police officers, a fact which Koyomi generally keeps secret to avoid problems. He realises that his relationship with Sodachi must go further yet and there is more he still needs to remember.

S1 E5 • Sodachi Lost, Part 1

Hanekawa reveals her concerns about Ougi as she and Araragi go to visit Oikura.

S1 E6 • Sodachi Lost, Part 2

Araragi and Hanekawa visit Oikura and learn the painful story of her family's past.

S1 E7 • Sodachi Lost, Part 3

Ougi claims to have figured out the whereabouts of Oikura’s mother and, in her own way, helps Araragi and Hanekawa to solve the mystery.

S1 E8 • Shinobu Mail, Part 1

Koyomi Araragi waits in the ruins of the cram school to ask Suruga Kanbaru for help, a request he hopes she will refuse.

S1 E9 • Shinobu Mail, Part 2

After a hurried departure from the cram school ruins, Koyomi and Suruga head toward the meeting place, only to encounter some difficulty along the way.

S1 E10 • Shinobu Mail, Part 3

Having finally arrived at the meeting place, Koyomi and Suruga find an unexpected person waiting for them. Before their reunion can take place, they must face an unexpected foe!

S1 E11 • Shinobu Mail, Part 4

The group relocate to the North Shirahebi Shrine where Izuko Gaen tells them the story behind the location and the effect Shinobu’s first minion had on it.

S1 E12 • Shinobu Mail, Part 5

Koyomi is confronted by Shinobu’s first minion, the original apparition killer. But instead of starting a battle, the samurai makes a simple request.

S1 E13 • Shinobu Mail, Part 6

As Koyomi prepares for his duel, he learns of the crisis that Hanekawa is facing and must decide what battle he should fight.