Many years ago, zombies took over the surface of the Tokyo, forcing humanity to retreat underground. Over time, much knowledge of the world before has dissolved into myth and legend, with many of the eldest survivors dying off. One girl, Hisako, is fascinated by her family's stories of what life was like before the zombies, particularly about a mysterious place called "School" where friends would gather to learn and play. Spurred by her natural fighting instinct, and inspired by these stories, she sets out to liberate the surface and bring as many friends as she can make to school, no matter how many zombies and other monsters get in the way!
This game provides examples of:
- Ability Depletion Penalty: Running out of stamina requires you to wait until enough amount has been regenerated before you can peform an action that requires it (such as attacking or dodging). Hisako also verbally points this out whenever you act while the stamina bar has just been depleted.
- Absurdly Spacious Sewer: And not just sewers! The vast underground maps that comprise a majority of the game are simply massive, bordering on hollow earth scale! Justified since the diggers of Akihabara have expanded the tunnels over the years.
- Action Girl: Hisako was a zombie-slaying badass even before she made it her mission to take back the surface, with her introductory cutscene having her obliterate a group of zombies with her bare hands.
- The Aesthetics of Technology: Hisako's weapons, especially the two-handed melee weapons, have a chunky, brutal, and almost overly complicated look to them. Think of the styling as similar to the weapons shown in Warhammer 40,000.
- After the End: It's been 78 years since the Zombie Apocalypse drove the population of Tokyo into the underground.
- Anti-Frustration Features:
- Currently-equipped Attachments aren't bound to a specific weapon per-se, which means changing your weapon doesn't remove them as they're slotted into the weapon type instead. This eliminates the worry of having to unequip and re-equip them over and over, though Weight management would still be a concern.
- You can mark weapons and Attachments as "Valuable" or "Trash", and there's specifically a feature that lets you automatically select all Trash items to be quickly sold for some cash.
- Autosave: The game automatically creates a backup save whenever you exit to the main menu via a Save Point. It can be specifically accessed via the Load option.
- Badass Adorable: Hisako is adorable as they come, but can slay zombies left and right using anything from swords to chainsaws to a variety of guns and launchers.
- Beef Gate: You may encounter enemies that are above Hisako's level, as indicated by a "Strong Enemy" skull icon beside their names. There's nothing stopping you from trying to fight and defeat them, but this is usually the game's way of telling you to explore other areas and grind more levels first before you can properly proceed.
- Bland-Name Product: Upon arriving at the surface via Shinjuku, one convenience store in the background, named 9-Nine, has the trademark colors and design of 7-Eleven.
- Chainsaw Good: After progressing through the game, Chainsaws become available to use. They provide low damage and no combos, but deal many hits at an incredibly fast rate, making short work of close-range targets at the cost of quickly wearing down the weapon.
- Clothing Damage: Taking enough damage puts Hisako in a danger state, as displayed by her clothes being torn apart (but still maintaining her modesty).
- Continuing is Painful: Dying takes you back to the previous Save Point, though you'll lose 10% of your current money.
- Cool Train: The subway train Hisako uses to navigate the underground regions. It's got stylish trimmings, plenty of armor, can blast through debris and other obstacles, and makes a Dynamic Entry every time it arrives at your destination.
- Cyborg: After defeating the second major boss, "the Steel Mutant", you discover that the giant mutant is robotic inside. You learn that the mutant invasion that forced the people of Japan underground aren't the only hostile force, and some third party is making cyborgs out of the mutants.
- Dynamic Entry: Whenever you arrive at your destination, the subway train accelerates with enough momentum to leap high and slam down its cars, crushing the mutants that are roaming in the railway.
- Earn Your Happy Ending: After a hellish journey through many hazardous underground regions, as well as zombie-infested Tokyo, and corrupted military machines and leaders, Hisako succeeds in the destruction of all zombies on the surface, finds an old school building, and gets her wish of rebuilding life on the surface and going to school with her many new friends.
- Effortless Achievement: Several achievements are awarded for simply going through the scripted tutorial segments in the first area. Specifically, there are two separate achievements for reinforcing and modifying a weapon for the first time, which can be achieved within a few seconds in the same tutorial segment.
- Elevator Action Sequence: After activating the elevator in Shinjuku, you have to fight waves of mutants inside until the elevator arrives at its destination.
- Equipment Upgrade: Reinforcement increases a weapon's level and stats. Modification adds or changes a weapon's bonus ability. These mechanics require their respective Reinforcement Gears or Modification Gears with each upgrade.
- Fanservice: Whenever the game cuts away from the action to show artwork of a cutscene, if it features a female character, 99% of the time it's going to feature plenty of barely obscured nudity.
- Fission Mailed: Upon arriving at the surface for the first time via the Shinjuku station, you will be ambushed by high-level mutants (one of which is clearly indicated as a Level 43). While you can fight them despite only having cleared the starting area at that time, the game will proceed normally if Hisako's HP is depleted, triggering a cutscene where she meets a mysterious silver-haired girl, and gets transported back to the main train. This would then properly unlock the next area you have to go to make progress with the story.
- Game-Breaking Bug: Usually, falling into a bottomless pit takes you back to a safe ground or platform where you last stood. Unfortunately, this mechanic may sometimes glitch out and send you far back to a previous Save Point instead. If this happens, you may be unable to transition between rooms properly (for example, elevator platforms won't move Hisako to the next floor). Fortunately, closing the game and/or reloading your save file can fix this bug.
- Healing Checkpoint: Interacting with a Save Point fully restores your HP, Stamina, melee weapon's durability, and ranged weapons' ammunition.
- Hint System: Random gameplay tips appear on the loading screens that feature Hisako sleeping in the train. Depending on how fast the game loads, you may not even get to read the full scrolling text.
- Infinity +1 Sword: The various unique weapons found in the game are mostly underpowered and quickly go obsolete on levels higher than where they were found. The best weapon in the game is whatever you crafted that used a weapon of Ultimate quality and whatever powerful abilities you favor and add to this weapon.
- Legendary Weapon: There are few unique weapons with a storied history and unique abilities. An example is the Flying V, which was a guitar used by a heavy metal guitarist who gave his life fighting hordes of zombies so people could safely escape and when used it created a large dome of sonic energy to hit everything in the radius.
- Limited Loadout: Hisako can only equip one of each weapon type; a melee weapon (Sword), and two ranged weapons (Machine Gun, Launcher). Each weapon type can only have up to two Attachments. Even then, there's an overall Weight limit that determines how much can you optimally have at once, and each weapon and Attachment has its own Weight value.
- Metroidvania: Not a pure example. There is a labyrinthine level design, lots of keys and micro backtracking, but no new abilities are gained to aid exploration. Also the game is stage-based, though you can go back to any level whenever. However, there is never any real reason to do so as they can be completed on a first trip and enemies don't level up, so there is no grinding or raids.
- Mutants: People have been mutated by an unknown virus into zombie-like mooks and huge monstrosities. So many were created that the mutants would drive the remaining humans deep underground for 78 years. The virus didn't just infect humans, animals and plants were also affected — this ranged from the harmless such as edible fish sprouting legs, and vegetables developing eyes, to far more dangerous creatures such as venom-spitting plants and Giant Spiders of various sizes and abilities.
- Nice Girl: When she's not eviscerating zombies by the dozen, Hisako is incredibly cheerful and optimistic about her mission to liberate the surface and go to school, and the prospect of making new friends with the various NPCs she meets fills her with more excitement.
- Notice This: Hisako verbally points out a rare item in the Store if it appears, aside from that item's font color also making it noticeable.
- Real-Time Weapon Change: Hisako can easily swap between her three equipped weapons in real-time with just a button press or mouse scroll.
- Replay Mode: The Gallery submenu of the Student ID Notebook lets you rewatch any previously-unlocked animated cutscenes.
- Respawning Enemies: Enemy encounters in the station will reset or respawn whenever you interact with a Save Point.
- Rewarding Vandalism:
- You open treasure chests or caches by smashing them with your weapon.
- Some objects stuck in the environment can be destroyed to drop something, such as a boulder hanging on a cliff in Shinjuku dropping one of the game's earliest souvenir items.
- Shout-Out:
- The splash screens when introducing a new large enemy type are very reminiscent of Borderlands.
- The "Human Cocoon boss bears a strong resemblance to recurring Castlevania'' boss "Legion".
- The large walker mechas later in the game have a more BattleTech look to them than traditional Japanese mecha. The first one you encounter is even called Assault Mech.
- The mysterious woman (Fow) Hisako meets upon her first arrival to the surface is essentially a female Sephiroth. Complete with a One-Winged Angel form later on.
- Socketed Equipment: You can equip up to two Attachments per weapon. These provide stat boosts or additional effects, but each one also comes with its own Weight value.
- Speed Echoes: Hisako creates blue after-images behind while she's sprinting.
- Sword Beam: Amongst the various weapon mods that can be found or bought, one of the most powerful is a series of short-ranged energy waves that occur when you do a melee attack. This ability is especially dangerous on chainsaw-type weapons due to its constant attacks.
- Video Game Dashing: Hisako can sprint at the cost of her stamina being slowly consumed.
