well, this sucks, I thought I live in the future
here we go: Mask/Goggles/Diving headgear by Nitori Tech

Stuff:
Since I didn't get any time to clean it whatsoever or edit it...
General gameplay system:
1. Air System, much like MOF, air represents how much air is left for the player, any player with no air left automatically dies, when respawn she gains an additional bomb, and loses 1 power (4.00 -> 3.00) and have a green air meter indicating she has full air , this air meter will gradually decrease until red, and then when empty, player dies.
2. Air Bubble System - enemies generate friction through firing danmaku, friction creates magical air bubbles which the player must capture in order to extend their air meter.
3. Playable Characters: Marisa, Reimu, Iku Nagae, and Suwako. (Suwako and Iku Nagae do not get affected by the Air System as bad as Marisa and Reimu, but are slower, and their powers more towards shotgun and close distance)
- Reimu - uses orbs that ram the enemies, massive orb as bomb. standard talisman bullets, slower bullets but smallest hitbox.
- Marisa - Starlight Reverie, standard laser from surfboard, may switch to focused laser in pinpoint form. (1 thick stream)
- Iku Nagae - a close distance bomb with her drill, spread type electric 'eels' projectile, semi-tracing projectiles.
- Suwako - shotgun type, non spread, weak when distanced, slow but small hitbox, has the biggest air meter and can literally ignore air bubbles system if played well. Massive frog bomb.
Nitori x Marisa again - the team of friendship never fails, while lacking the hakkero's granted Master Spark, Marisa can summon her Starlight Reverie to her aid, and with her broom gone, it is up to the Kappa to come up with an ingenious way to waft through water... so how about a surfboard? BUT SURFBOARDS WORK ON WATER NOT IN IT, well, not this one. Utilizing its streamline shape, Marisa retains most of her speed but especially forward, less sideways which makes her movements a bit limited. Utilizing the same system from her SA bomb, the shield that neutralizes enemy projectiles, Nitori is able to make the suit, which resembles the shield but is used to repel water instead of bullets. This means Marisa when moving is actually floating in an air bubble like protection, surfing through it while shooting at the enemy with her lazors.
Marisa's fins improves her movements when she loses the surfboard (which is changeable once she runs out of air (when the air meter goes to red)
Only Marisa has a diving mask of sorts that gives her one last dose of oxygen until she dies of suffocation, which is GLUGG BLOBBBB EGGHHGGGRHHIAMDROWNING. She switches to her fins for maximum maneuvering power, allowing her to use her abnormal speed much like Trance mode. This however, means she will go down really fast unless she finds some air, some enemies deliberately don't give air until they die, making it all the more difficult.
During Desperation Mode (red meter) other players have other types of moves, but Marisa is about heightened speed and maneuverability. They all last approximately 10 seconds.
Reimu gains a temporary Yukari barrier which gives her some extra projectiles, heightened power that last 6 seconds out of 10 seconds of remaining air.
Iku Nagae gains Tenshi's rocks, more attack power, but slows down even more. not ideal, but at close range can be deadly.
Suwako gains Sanae's faith, changing her bullet type to spread carpet bombing instead, ideal for killing enemies that just entered the screen and grabbing some oxygen.