The airshare did not help for long but after what feels like an eternity they finally see the light of the submarine ahead of them. Air! - at least for one of them at a time since the air chamber of the submarine is just large enough for one person.
Amy and Blaze both are determined to let the other take the gasp first but they are both clearly at their limits. Eventually it was Amy who persisted the longest on letting Blaze breathe and the catgirl gasps hard inside the helmet.
The sound of sucking such badly needed air is too much for Amy though and her lungs finally give out. Another, much more aquatic gasp can be heard when she shakes on the spot, coughing as her body instinctively refuses to let the water into her lungs.

Now it is time for Blaze to react fast and barely having taken more than one breath, she dunks herself out of the submarine again to grab Amy. Seeing that she is too disoriented to use the submarine now, the only thing she can do is cover her mouth with one paw to prevent water from seeping in.
With an impressively act of effort, Blaze manages to pull the cat girl ont he verge of unconsciousness, all the way out of the cave and starts ascending.
Torrents of bubbles leak from her lips when they are nearly at the surface but eventually they breach it.
Coughing vigorously they both barely can breathe but eventually they start to recover. This truly had been a dangerous dive... and they still have to return to the instable cave to retrieve the crystal before someone else does!

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This is a comic that was on my mind for literally ages.
Thank you https://www.deviantart.com/uwdennis for realizing it entirely! ^w^