In the full game, after beating Story Mode for the first time, a new difficulty mode may be unlocked: 1980s Mode. This mode can only be accessed through a save file that was used to beat the game. Currently, the mode can be accessed directly from the title screen, before the main menu has even appeared.
In 1980s Mode, the main character is Ryoba Aishi, Ayano's mother, who is the yandere girl featured in the Mysterious Tapes. Her appearance will resemble the Ayano from the save file that was used to start 1980s Mode.
This mode only has technology that was available in 1989, along with stricter school rules. There is no internet, smartphones (students call the police using the landline phone in the Faculty Room), Info-chan, or anything else that did not exist prior to 1989. The smartphone is replaced with a notepad. There is a Yakuza in this mode, unlike in Story Mode. There is an optional filter that makes the game look grainier and older, to help represent the fact that this mode takes place in the 1980s. Basement Tapes 1 to 9 are the epilogue of 1980s Mode.
The objective of this mode is to defeat ten rivals, like in Story Mode. However, the plot of 1980s Mode is not as elaborate as Story Mode. For example, all the events between Jokichi and the ten rivals are the same, but with different dialogue.
Differences to Story Mode
- The background music was completely remixed/remade to match the 80s style.
- Because smartphones did not exist in 1980s, the pause screen was changed from a cellphone to a notepad. Instead of students calling the police on their phones, they will call the police on the landline phone located in the faculty room instead.
- All Student's Profile in the pause screen are loaded up at the start of the game, as you cannot take pictures with a phone.
- Ryoba's room is different from Ayano's room (2022), and the video game console was using "Makunuru", and it similar of Nintendo System Entertainment.
- Info-chan did not exist, meaning it is not possible to pay info points of the schemes' steps. However, all schemes are unlockable at the start of the game. However, some of the schemes must be unlocked.
- Ryoba is not threatening to Kocho Shuyona in 1980s Mode. If she encounters him, Kocho talks to her in a friendly way while in his office and will not try to tase her if she is close enough to him. But he will tase Ryoba if he sees her carrying a weapon or a corpse in front of him.
- The removed students that were previously removed (such as the Rainbow Students) now appear in 1980s Mode.
- Some of the electronics (such as the radio) are redesigned so it can fit the style of the 1980s.
- All students council members were male in 1980s, and they will turn around if they hear Ryoba's footsteps.
- The calendar screen is now "VHS aesthetic effects", and there's also a new menu called "stat" where the player can see their actions (Such as Homicide) in the last week.
- Ryoba will now be able to interact with the Yakuza at the town at night. However, the Yakuza will not speak with Ryoba, unless she completed Togo Atatsuma's task.
- The students with the "Snitch" persona will run to the faculty room and call the police on the landline phone if they discover a corpse or witness murder, and will stay there until the police arrive. This makes it impossible to kill them.
- The Journalist will be investigating Ryoba's suspicious behavior while walking in front of the school gate. If he sees Ryoba kill someone, he will quickly run up to her and pepper spray her, resulting in a Game Over.
- The Sociology Classroom was in place of the Gaming Club in this mode.
- The Info Club has been changed into the Newspaper Club.
- There is a grade you will receive at the end, depending on the way you played the game.
- The music playing around near the incinerator is located where the delinquents hang out is different.
- The Saikou computer isn't present at Meeting Room and the student council room.
- The player is unable to use debug commands or easter eggs in this mode.
- Sumire Saitozaki (Tutorial rival)
- Kaguya Wakaizumi (First rival)
- Moeko Rakuyona (Second rival)
- Honami Hodoshima (Third rival)
- Sumiko Tachibana (Fourth rival)
- Ritsuko Chikanari (Fifth rival)
- Ai Doruyashi (Sixth rival)
- Teiko Nabatasai (Seventh rival)
- Komako Funakoshi (Eight rival)
- Chigusa Busujima (Ninth rival)
- Sonoko Sakanoue (Tenth and final rival)
- Before the events of 1980s Mode, there was a murder at Akademi High which prompted the school to force faculty members to undergo self-defense training before the player starts 1980s Mode.
- The idea for 1980s Mode occurred when someone complained that they did not like Info-chan and wanted a mode without her.
- YandereDev would like help from volunteers to make period-correct outfits and hairstyles for the 1980s.
- This mode features a brand new student body with a different configuration of colors and accessories.
- The Info Club room is the Newspaper Club in this mode.
- The Journalist appears in front of the gates at school and in multiple cutscenes.
- Senpai's parents do not appear in this mode.
- The events of the Story Mode are partially determined by the events of 1989, so there will be a "canon" way to eliminate each rival. If the player chooses to go with the canon elimination methods, then the Mysterious Tapes are proven true.
- This mode features the death of Sumire Saitozaki, also known as the Phantom Girl.
- She is killed in the tutorial to avoid a time paradox.
- This mode features the previous Delinquents, the removed rainbow students, the Study-Kun boys and Witness-Chan, who is now named Ui Tunesu. YandereDev said that if the framerate is more stable enough and there is more room for more students, then the rainbow students will be in Story Mode, and if not, then they'll stay in this mode. 
- This mode is meant to be the most difficult mode. It may include the player getting a Game Over if a witness escapes, since in the Mysterious Tapes, the yandere of 1989 was arrested with no hard evidence.
- YandereDev has stated that he will attempt to give this mode the same vibe as "a peaceful countryside Japanese town in the late 80s".
- This mode is ten weeks long.
- The outcome of this mode will not affect the story.
- Genka Kunahito's mother appears in this mode.
- The overwhelming majority of the new music in 1980s mode was created by one person, CameronF305. 
- There is a 1980s Mode mod based on the information YandereDev has revealed. However, it isn't canon, as the real mode has been released.
- While passing time, Ryoba looks at a photo card of Jokichi, rather than a phone.