A unique twist on Tower Defense games where the "tower" is just an ordinary person. Each stage has Sandy as the Damsel in Distress who is chained to an iron ball to plummet to the bottom of different flooded locales, drowning her if she's not rescued fast enough. You play as her best friend, Natica, who can speed up the unlocking process of Sandy's cuffs. In the meantime, she can give Sandy a mouth-to-mouth treatment to help her last longer underwater up until her she's freed from her restraints. Natica also brings with her a harpoon to defend Sandy from the ravenous fish and sharks that attempt to nibble and bite her when they get close.
Killing the fish nets you coins, and getting enough coins raises Natica's level, allowing you to select from a list of skills she can gain that will help to make rescuing Sandy easier, such as faster swimming, an invincible swimsuit, and even having Sandy defend herself against the fish for a moment. The more coins you collect, the more skills you can get.
Beating each level treats the player to a piece of Fanservice artwork of the titular duo, which either illustrates their situations and actions in the game, or has them in a Slice of Life moment unrelated to the gameplay.
Natica and Sandy was originally temporarily available during a Christmas Eve event Fox hosted in 2017. In 2019, the game made a return as a part of the Fox Eye Limited Game Collection, alongside 4 other event games for the fans that missed them. The following Christmas Eve of 2018 temporarily released a solo, 3D followup for Natica titled NATICA STAR SPLASH, which has also been included in the Limited Game Collection. The Japanese and English version of this collection can be purchased at DLsite.
Natica and Sandy: Underwater Rescue contains examples of:
- Anti-Frustration Features: By way of Fox Eye's extremely minimal use of Super Not-Drowning Skills (due to it missing the point of the developer's Author Appeal), as soon as Sandy is released from her cuffs, she no longer consumes oxygen. So unlike the case of Aya and Yuu in Aqua Cube, you won't have to worry about her drowning at anytime during her own swim towards the surface even if her Oxygen Meter was almost completely depleted.
- Art Evolution: All of the game's artwork has gotten an absolute breathtaking upgrade in the game's Updated Re-release in the Fox Eye Limited Game Collection, though the original 2017 version of the artwork can still be unlocked for comparison's sake. For starters on how much has improved, compare the 2017 artwork of the titular duo for the the title screen◊ to the page image of the title screen from the game's 2019 Updated Re-release.
- Ascended Extra: Natica first appeared in a previous event game in 2015, Slide Loop Puzzle, to debut as one of the mascots of the then-upcoming Fox Eye ABYSS division (which was largely advertised by the circle with the announcement of BLUE GUARDIAN: Margaret). She then later on starred in her own NSFW mini-animation, Underwater Pinch of Natica!, where she was put in the same situation that she must constantly save Sandy from in this game, except Sandy is nowhere to be seen, and the animation ends with Natica drowning. As of the Fox Eye Limited Game Collection, both Slide Loop Puzzle and Underwater Rescue have retroactively become the first instances of Natica appearing in a purchasable game after being a Fox Eye character that was only limited to appearing in artwork and Christmas Eve event releases. However, she has yet to represent an actual ABYSS title.
- Sandy, herself, originally appeared in a 2012 event game, preceding her friend in Fox Eye's entire roster by 3 years.
- Author Appeal: A name like Underwater Rescue obviously shows that this Fox Eye game doesn't have any dangers of drowning in it, right?
- Auto-Revive: One of the unlockable skills is an Elixir that revives Natica with half of her Oxygen Meter after she drowns. Getting the second Elixir skill auto-revives her with a full meter, instead.
- Back Stab: Played straight and inverted. Initially, Natica's harpoon does more damage to fish if she strikes them from the back. Over time, the player can unlock skills that further increase the damage her harpoon does from behind, as well as the front, separately.
- Blade on a Stick: Natica defends Sandy from ravenous fish by stabbing them with a harpoon. There are skills she can unlock that separately increase the damage the harpoon does to the fish from either in front or behind them, and the SP Swimsuit powerup also increases the harpoon's power as well as its length.
- Callback: This game is, in essence, a downscaled 2D version of Fox Eye's 2008 game, Aqua Cube. Both games involve one character freeing another one from an underwater restraint before they drown. Both games use two Oxygen Meters for each character and utilize the trope Underwater Kiss to transfer oxygen between characters. The only other major difference is that Aqua Cube is a Puzzle Platformer, while Underwater Rescue is a Tower Defense (with Sandy being the "tower", per se).
- Chained to a Rock: Each stage has Sandy chained to an iron ball and sent plummeting into a Drowning Pit for Natica to rescue.
- Clothing Damage: The unlockable artwork for Level 1-2 makes Sandy a victim of this by the piranhas. Level 1-3's artwork induces this on Natica, as well. They both suffer this at the same time in Level 1-2's artwork in the game's Updated Re-release in the Fox Eye Limited Game Collection.
- Counter-Attack: One of the unlockable and upgradable skills reduces the fish's health to a fraction of their full health each time Sandy takes a hit from each of them, making them easier to clear out once Natica swims back to her aid. The first upgrade reduces their health by 25%, while the second upgrade raises that to 50%.
- Damsel in Distress: Each stage has Sandy trapped underwater. You use Natica to unlock her chain and set her free before she drowns.
- Difficulty Levels:
- Drowning Pit: All of the stages in this game take place in one of these, as the premise is for Natica to save Sandy from them before she drowns, all while managing not to drown, herself.
- Expy: Now that Natica has gone from wearing a fake mermaid outfit with seashell pasties◊ in her Underwater Pinch of Natica! animation to getting her own blue one-piece swimsuit in this game (see the page image above), it has become much easier to mix her up with Marie from Holdover when she's in her own blue swimsuit. Their major differences are their hair decs, and Natica lacking Marie's anti-buoyant computer anklets, while their only other differences are in their slightly-different skin tone, hair tone, and hair length. Natica and Marie's similar looks (along with the looks of Rico from Blue Port) were already lampshaded and discussed by Fox in some crossover artwork◊ made prior to this game.
- Fanservice: The girls themselves are wearing skintight swimwear like several previous Fox Eye heroines have been known to do. Your reward for beating most of the stages tends to have artwork of Natica and Sandy in the nude, either from Clothing Damage or of their own volition (albeit in a Barbie Doll Anatomy kind of way).
- Hair of Gold, Heart of Gold: Best friends Natica and Sandy have both contributed into Fox's rather-lengthy list of cute blonde heroines. The game's general theme is that one friend trusts and depends on the other to save her life.
- Instant-Win Condition: Just like with Aqua Cube, a stage can't be beaten until both characters come back up to the water's surface to breathe air. This means that Natica can still drown and give the player a Game Over even after successfully freeing Sandy.
- Last Chance Hit Point: Compared to the Anti-Frustration Features for Sandy mentioned above, this game has a slight "grace period" between when Natica drowns and when the game acknowledges it as a Game Over. Drowning paralyzes her body from the lack of oxygen, but if she was swimming towards surface when this happens, her remaining momentum when she freezes up can be enough to still carry her to the surface if she's close enough, allowing her to catch a breath even from a completely depleted Oxygen Meter, preventing a Game Over and/or saving the use of the Elixir skill in the process.
- Leotard of Power: The SP Swimsuit is an unlockable skill that will then randomly spawn from defeated enemies. Picking it up makes Natica invincible, draw the fish's attention towards her instead of Sandy, and also increases the power and length of her harpoon for 10 seconds. This is a huge step up from Fox Eye's previous use of this trope.
- Our Mermaids Are Different: Mermaids exist in this games setting, and Natica loves them to the point of dressing up as a mermaid to swim with them. The one fatal problem with this is that she cant breathe underwater like they can. So not only is she unable to speak with them due to having to hold her breath, she ends up confusing real mermaids◊ when she starts running out of air.
- Oxygen Meter: This must be a Fox Eye game, after all! For the first time since Aqua Cube almost 10 years ago, this game has you manage two at once: Natica must swim back up to the surface to catch a breath, while Sandy relies on underwater kisses from Natica until she is finally freed in order to complete the stage. Either girl getting bitten by fish makes their own meter drop faster. One can unlock Oxygen skills that can make Naticas Underwater Kiss more effective at feeding Sandy air.
- Piranha Problem: Both girls love swimming with the fishes, but the only fish they encounter in this game want to eat them.
- Sexy Santa Dress: In celebration of this game being a Christmas Eve event, Sandy sports one.◊
- Shark Pool: The underwater places Sandy is tossed into are also full of biting fish that quickly try to nibble at her and her swimsuit. Later levels start throwing actual sharks into the mix. Good thing Natica has a Blade on a Stick.
- Temporary Online Content: The game was available for free on Fox's FC2 page for a 2017 Christmas Eve event gathering. In 2019, the game made a comeback as a part of a purchasable Compilation Rerelease called the Fox Eye Limited Game Collection.
- Thanking the Viewer: The last three pieces of unlockable artwork essentially have Natica and Sandy do this to the player by wishing them a Merry X-Mas.
- Threatening Shark: These guys start appearing in later stages, with the tougher ones being bigger and purple.
- Tower Defense: That is to say that Sandy herself is the "tower". Until her lock's timer reaches zero, Natica must feed her oxygen via mouth-to-mouth to keep her from drowning, and protect her from the vicious biting fish that plague the submerged areas she gets stuck in. Natica can also tinker with Sandy's cuffs to speed up the unlocking process. The stage is beaten after Sandy is released, and both she and Natica surface for a breath. The game's main challenge is managing between keeping Sandy safe from harm while also making sure that Natica, her supplier, doesn't lose her own life in the process.
- Underwater Kiss: Until Sandy is freed, Natica performing this move on her is the only way Sandy can keep holding her breath underwater, but this is at the cost of Natica's own Oxygen Meter. So doing this too much without surfacing for an open breath will only make Natica drown, instead.
- Updated Re-release: The version of this game that's included in the Fox Eye Limited Game Collection was the first to be released in English, and also upgrades all of the unlockable artwork. Much of it provides even more Fanservice from the titular duo than previously.