Childhood Friends!! It is a friendship that spans from early childhood. A childhood friendship between a pair of boy-girl, in a sense, is a fantasy—
In the infamous dungeon, Wyrm Hell, seventeen year-old swordsman Van fights his way down to its one hundredth floor, where resides its most dangerous boss, the Dragon King Obsidian. Once face to face, the Dragon King... transforms into a teenage dragon girl and the two of them spend the day hanging out.
Adventurer Van Sirius and final boss Ryuuka Obsidian have been friends since they were seven, and Van makes monthly trips to the dungeon to visit and deliver goodies from his mother while Ryuuka's minions look on and enjoy watching their relationship develop.
The monthly visits are set to come to an end, however, as Van reveals that he's joined the adventurer's guild in the town near Wyrm Hell, meaning he'll now be able to come visit Ryuuka every day.
Dungeon No Osananajimi by Yasuhisa Kuma is a fantasy Slice of Life in which a pair of unusual childhood friends hang out regularly.
Dungeon No Osananajimi contains examples of:
- Art Shift: The four members of the Dark Board look like genuinely terrifying monsters when discussing business, but look a lot nicer and softer when it's just them being Date Peepers.
- Audience Surrogate: The four members of the Dark Board pretty much reflect different points of view of the audience enjoying the view of childhood friends. From just enjoying the sweet wholesomeness of their friendship (Wul-kun), shipping them hard (Mino-san), providing ways to enable progress (Orkkun), or wanting to see things get sexy (Harpy-san).
- Bad Boss: Ryuuka can be this, but it's usually because the four Board members deserve it. When Van stated he needed to get some items from the dungeon to rank up in the Guild, he pulls out a paper that shows body parts of the four are worth a good amount of money. Ryuuka just points to them and says "have at them".
- Benevolent Boss: Mino-san does not like Succy the Succubus due to a combination of a general dislike of succubi and because her actions inadvertently got between his shipping of Van and Ryuuka. However when Succy, oblivious to how Mino-san feels about her, confesses to feeling inadequate to the task being a monster of Wyrm Hell, he gives her sincere advice on how to turn her abilities, pros and cons alike, to her advantage. As Mino-san does this, there's a note next to him explaining that he doesn't allow his personal feelings to interfere with his work. The chapter ends with Succy seeing greater success, using her attempts to seduce incoming adventurers as a distraction to help other monsters rather than as an attack in and of itself.
- Blood Knight: Golde has conquered numerous dungeons across the world and yet never takes any of the treasures within. It's because he loves the challenge of fighting strong opponents more than any riches he could earn doing so.
- Blunt "Yes": After Van reveals that he moved to the village nearby so he can see her everyday now, Ryuuka coyly asks if the reason he did that is because he gets lonely not seeing her. He just flat out says he does, much to her stunned surprise.
- Childhood Friend Romance: Not Ryuuka and Van, though the signs of it potentially developing are there, but rather Golde and Sylvia. Despite Sylvia's youthful appearance, she and Golde are the same age, have known each other since they were children, and are married with a teenage daughter of their own. This revelation immediately sets the Board of Directors to imagning Ryuuka and Van as a married couple with children.Narration: The four idiots found their utopia.
Mino-san: I just can't get enough.
Orkkun: So that's where paradise lies.
Harpy-san: I hope they have at least 4 more.
Wul-kun: I want to be part of their family.
- Childhood Friends: The premise of the series is that the Childhood Friends of the title are an adventurer and a dungeon's final boss. Van regularly crashes through Ryuuka's dungeon for the sole purpose of hanging out with her. Chapter 2 shows that they met when they were seven years old. Van's family took care of Ryuuka after she got separated from her family, and Van helped her reunite with her parents.
- Curb-Stomp Battle:
- Van can power his way through the 100 floors of Ryuuka's dungeon in no time at all. In fact, Mino-san notes it's very easy to know when it's Van coming because the announcer that alerts the dungeon to intruders informs everyone that a floor has been breached one after the other in rapid succession. The Board of Directors has basically given up trying to actually stop Van, only trying to because it's literally their job and setting goals like "hold him for 10 minutes."
- In chapter 9, Van curb stops the World's Strongest Man, Golde. He's able to do a Bare-Handed Blade Block with two fingers of the hand he's holding his sword with to effortlessly stop his opponent's own attack then floors him with one punch.
- Dungeon Bypass: Chapter 5 opens with a description of how Van makes his way through Ryuuka's dungeon on a daily basis: Brute Force. Van's clearly established to be strong enough to take on all the monsters en route, but this sequence also shows him charging straight through the obstacles and traps, such as puzzle doors, in exactly the same way.
- Everyone Can See It: No one except Van is fooled by Ryuuka's insistence she has no romantic feelings for Van. The Board are calling her out on it as early as chapter 2, and regularly enjoy watching them interact. In chapter 10, Sylvia calls it obvious when Ryuuka acts with confusion to her promise to root for them.
- Green-Eyed Monster: Ryuuka becomes enraged when she sees Van Bridal Carry Sylvia. Sylvia realized her feelings for Van because she knows Golde reacts the same way when guys flirt with her.
- Had to Be Sharp: Since Van doesn't get a free pass to the bottom of the dungeon, he had to fight his way through all 100 floors every month for ten years just to spend time with his childhood friend. This being a dungeon where the average Adventurer rarely makes it to Level 45 at best and only the most high ranking monsters in the dungeon are aware of his and Ryuuka's friendship. Because of that, he is incredibly strong that he can now speed run the dungeon in minutes.
- Hand Signals: Ryuuka and Van have their own sign language they can use to talk to one another that's developed enough to have an entire conversation without either speaking a word out loud.
- Last-Second Word Swap: Ryuuka has one when she gives her excuse as to why she is constantly spying on Van.Ryuuka: What if he has another gir... friend.
- No Hero Discount: Despite Van being the Dungeon Master's childhood friend, he still has to challenge all 100 floors every day if he wants to see her like everyone else.
- Mistaken for Flirting: Chapter 5 introduces Succy the Succubus, who tries to seduce Van while he's making his regular charge through the dungeon to visit Ryuuka. However, among the dungeon's monsters only the Board of Directors know the nature of their relationship. This causes Mino-san, out of a combination of protecting Ryuuka's secret and being offended at Succy trying to get between Van and Ryuuka, to charge Van, lose, and use that as an excuse to let Van proceed to Ryuuka. Succy, unaware of what's going on, sees the whole thing as Mino-san leaping into the fray to protect her and comes the conclusion that he has a thing for her, oblivious that he's actually very annoyed at her.
- Overshadowed by Awesome: The Board are actually very powerful monsters, with Golde even commenting they are stronger than even Boss Ranked monsters in other dungeons he has conquered. It's just that Van is so strong he beats them up in an instant and most of their onscreen time is focused on them being Date Peepers.
- The Peeping Tom: Chapter 4 features Ryuuka being given the chance to watch Van when he's not at her dungeon by way of a Magical Witchcraft Monitor, essentially a television set that gives Surveillance as the Plot Demands focused on Van. Despite a token protest, Ryuuka spends every moment Van's not physically with her watching the TV for days at a time, the narration going so far as to call her a complete stalker. The issue is ultimately resolved when Van, having noticed he's being watched but not sure how, starts glaring in the direction of the camera, and the sight of his angry face being directed towards her makes Ryuuka destroy the monitor.
- Punch-Clock Villain: The monsters in the Dungeon attack adventures because it's their job.
- Punny Name: Ryuuka Obsidian's name translates to Black Dragon.
- Schmuck Bait: Ryuuka fell for a Mimic Trap because there was a note in front of it "These are the snacks".
- Shipper on Deck:
- Ryuuka's top enforcers, her Dark Board of Directors, spend the bulk of their screentime quietly watching Ryuuka and Van's interactions, finding their relationship precious. Harpy, especially, is all for them upgrading their relationship. They don't even mind that Van will be able to start visiting daily, even though it means he'll also be beating the crap out of them daily since it's their job to at least try to stop him.
- Sylvia the mage joins in the on-deck shipping in chapter 10, when she's quick to notice the nature of Ryuuka's and Van's relationship and quietly tells Ryuuka she'll be rooting for them.
- Succubus in Love: Due to mixed messages, Succy the Succubus has grown feelings towards Mino.
- Suspiciously Specific Denial: The Board are not fooled for an instant with how much Ryuuka claims that she only sees Van as a childhood friend and nothing more.
- Take That!: Chapter 3 opens with the childhood friends playing The Game of Reincarnation, a parody of Game of Life in which players aim for the strongest rebirth. The game takes potshots at various other fantasy and isekai genre stereotypes, with Van getting kicked out of the hero's party and gaining a powerful revenge buff.Mino-san: I duuno what the youngsters like but there's no reason to get uppity about it. I mean look, the Lady Dragon Queen has such a happy face on.
Ryuuka: The heroine was NTR'd by an ill-mannered hero!! Mass-murder mode activated!!
Mino-san: Yeah screw that this is a terrible game.
- Thou Shalt Not Kill: Ryuuka enforces a strict "no killing" rule on her minions. It is for this reason that Wyrm Hell maintains a record of zero fatalities on both the human and monster sides.
- Tranquil Fury: Some of the plans the 4 subordinates do causes this for Ryuuka, usually ending with her gently smiling and hurting them in response.
- Tsundere: Ryuuka is quick to vehemently deny any romantic feeling whatsoever for Van, but regularly is shown becoming jealous when he interacts with other girls or blushing at fond memories of their times together, only to vehemently deny doing any such thing. Harpy-san outright calls her a tsundere in chapter 9.
- Weredragon: Ryuuka can freely change from a dragon form to a humanoid form that looks like a dark skinned teenage girl with four horns on her head. This is a skill she learned over time as she could not do it when she first met Van.
- World's Strongest Man: Chapter 8 introduces Golde, "The Legendary Man". He gets his names from all the legends that have sprung up in his wake. He's conquered dungeons all over and he's arrived to take on Wyrm Hell as he lives to take on powerful opponents. However even he can't do a thing against Van, who fights him to protect Ryuuka and wins handily.
- Younger than They Look: When Sylvia offers Golde comfort after fighting and losing to Van, the Board of Directors get up in arms about how Golde can get a young girl like Sylvia giving him such affection. They're shocked when Sylvia explains that not only are they married, they're both the same age.Board of Directors: That age gap is way too much!!
Sylvia: What? No, we're the same age. The same age.
Sylvia: We're both 35 years old.
Board: So young!!
Golde/Sylvia: We get that a lot.