You decide that of all the possibilities, attempting this partial escape you desire is best done with both her awake, and eager to play: any potential future escape of yours should be done no matter the difficulty ahead, so succeeding in the most difficult scenario would provide both experience and calm on future attempts. Also, you want to try while taking advantage of an occasion where your "owner" desires to have fun, and thus your escape will not anger her as much if you attempted it in a situation where she's less disposed to such antic; she would likely find you remaining with her despite your success to be a pleasant surprise, which would likely aid you in starting with the right foot your stay with her. 

So, with your plan ready, you snuggle up, and close your eyes, waiting for tomorrow's best possible time. The warmth of the place, combined with the rhythm of Shina's heartbeats and the motion of her breaths, help you give in to sleep rather quickly.

You're unceremoniously awakened rather early in the morning, with Shina in the middle of class: when she notices your little movements as you innately move around to accommodate yourself into a better position after spending an entire night curbed, she proves to be understandably unwilling to try playing with you either there and for the remaining time as school, being busy and all that.

Even if you had any latent grudge against her due to her treatment of you before, you wouldn't be such a jerk to provoke a scene, so either way, you would obey; first, you remain as still as possible, before drifting to take a nap for the time, for she promised you to play later. 

That promise timed for "games" arrives in the afternoon, with her at a café, and desiring to enjoy her coffee while you squirm around her breast: her precaution of being near the bathroom tells you would be free to act giving everything you could do without fear of reproach; this situation couldn't be better for your planned escape, so you make use of it without hesitation.

First off, you need to get rid of the bra that covers her chest: it's an impenetrable and unmovable obstacle to your goal. Thankfully, there is a surefire way to force Shina to remove it, and that's by making her climax: it would also teach you how best to make her cum from now on.

You get to work, licking and massaging all around you, instead of spending your limited stamina struggling towards the currently block exit. It's hard, for the girl doesn't hesitate to pull and pressure your body, actions that sap your energy with every attempt.

Yet you diligently keep your efforts up, taking small rest for a few seconds before continuing your work, provoking both louder and louder moans as well as making her milk surge in larger and larger streams. Inevitably, this growing crescendo of pleasure and milk reaches the tipping point, and as the girl makes the loudest series of moans yet, a mighty stream of liquids rushes forward, pushing you with it. It's powerful, yet short-lived, lasting a brief few seconds before it fizzles out.

Yet the first step was achieved: the giantess' bra was ruined, as she comments:

"Aww, look what you've done...it's a good thing I always carry a change of clothes. Well then, let us excuse ourselves to the toilet then."

Very quickly, she makes your "world" shake with every step and every sway of her large breasts, tightly held as they currently are. Yet even from within her, you can hear the noises of opening and closing doors, before the final shake she makes as she sits on the top of a toilet. Once there, she allows her boobs to sway free, while excitedly exclaiming this was now time to "play seriously". 

She wasn't lying: now in as private of a spot as she could have, she was free to focus her entire attention on each action of yours, instead of primarily working to keep her moans as low as possible as to make out a scene in this rather public space, thus she can pull and pressure you more constantly and more strongly.

This, combined with your lesser amount of remaining stamina, and the need for you to reach the outside of her nipple to have both fresher air and to be in reach of her G-spot which if caressed enough, would surely provoke a new orgasm for the girl in no time, made it for this final phase of your struggle to be the hardest: at one point you thought you would be forced to give up your attempt entirely, by how exhaustive and challenging it was becoming. Yet you didn't give up, and focusing the bulk of your remaining energy on licking and caressing the aforementioned G-spot proves to be a smart choice, for another mighty surge of milk rushes forward from within, shooting you away from her breast.

What follows is a brief moment of sheer terror, for you find yourself in freefall from what to you is a height comparable to dropping from the top of a skyscraper, approaching at lightning speed the hard substrate at its base. 

Yet your currently tiny size proves to be an enormous blessing this time, for your hit with the hard tiles on the bathroom floor leaves you without harm: you're not even dazed by the impact, an excellent detail to rely upon by potential future attempts. 

As you raise yourself, and take the opportunity your success has provided you to stretch out fully without any constraints (actions that your joints and muscles surely appreciate), you get to witness a gorgeous view: a cute girl, with her ample chest wide for you to state at, nothing hiding its sensual beauty. The fact that these comparatively small jelly-like mountains are just a part of a bigger and sensual individual grants this scene which you could have devised in your lewdest dreams an air of majesty your imagination would never have considered: and all this happening for real. To be sincere, this is another perk to add to your situation, bleak as it might overall be.

If you had any regrets about not taking the opportunity to run and hide instead of just waiting, the time to act upon them is soon over after a few precious seconds, Shina recovers from the climax, taking deep breaths before she opens her eyes and begins to speak happy, saying:

"That was good! Alright, time to put you back in my..."

The tone of her voice and the expressions on her face shift quickly from congratulatory pride to sheer panic as she exclaims:

"Hey! Where did you go? Come back here!"

"Down here, Shina! Down here!" you exclaim loudly while waving your arms in your attempt to gain the giantess' attention, for it is indeed time to return inside her chest, and quickly: the sooner you're back within the hair, the earlier you can begin to device what to do next.

Your actions soon bear fruit, as the gigantic girl quickly notices the small waving figure standing close to her: it's hard to ignore the male voice coming from below, considering its most likely source. 

She gasps when she sees you, standing still, and ready to be taken back. One of her hands quickly goes down and grabs you, rising through the air at high speed, before stopping you before the very face of the giantess, the first time since you met her.

She is looking at you with blushing cheeks and a happy smile, pressing you against her as she begins to give you what she thinks is a nice hug. She speaks, excited:
"Awn, I'm so lucky to have already such a loyal and loving pet! Didn't want to leave your beloved owner? Yes, that must be it..."

"Nah, not really..." you commented in a neutral tone, as you couldn't help but reply to correct the girl's assumption.

She must not have expected you to do that, for she quickly pulled you back while looking at you with curious eyes: instead of getting mad as what you could easily imagine could be considered "insolent" behavior from a tiny, she finds it curious. In a tone matching her eyes, she asks:
"Then...why did you choose to remain with me? You could easily run and hide from me while I was still recovering from the climax, right?"

"Correct, yet I had already decided for some time now that remaining with you is the better alternative: my size would limit me to this singular floor of this building, or any other for that matter, where I would have to spend the rest of my days skittering in the shadows, scavenging any leftovers of food and drink, while hoping never to be found by anyone, who mind you, could easily be worse than you. And you know what they say: better devil known than god to know," you respond.

Your direct and utilitarian reply makes clear to Shina the reasons behind your actions, making her a bit sad as she comments:

"Oh, I see..."

Seeing her like that, makes you feel somewhat sorry for her, despite knowing what kind of relationship she expects to have with you; so, you try to cheer her up a bit by saying:
"Well, there is also the matter that you're cute and sexy: it makes my job to please you a lot more bearable."

Your attempt, short and perhaps a bit brunt, nonetheless has the desired impact, as Shina brightens up a bit yet again, with her smile returning. And with a bit of blushing, she says:
"Awn, thank you, tiny gentleman, I appreciate what you did just know: it makes me happy to know that my pet finds me cute."

You decide to just look to the side instead of speaking further: you're still annoyed that she calls you "her pet", yet not enough to justify any discussion right now. You have already achieved to have a small chat with the girl despite how much leeway she has over you so that it's good on its own; didn't get punished for talking bad about her, at least for now.

Shina meanwhile takes your silence as a signal that this chat is over. She speaks again, saying:

"Well, this whole event has been rather fun, but you're likely exhausted, right my pet? So, why don't I put you back in your home, where you can take a nice nap before we try again later? I might be in the mood to play with you before dinner, hehe."

Following that, her hand brings you back towards her left nipple, shoving you back inside her breast.

However, instead of following this up by pulling you back inside, she looks at you momentarily, with a somewhat worried face. She then speaks, again:
"Before you go back home, I need to make something clear though: I appreciate your comments since they allowed me to get a clear picture of what was going inside of your little head yet...don't get any wild ideas, ok? You're my pet, and pets are not supposed to talk back at their owners, do they?"

Her tone carries her sentence with the weight of a weary command, with the core message clear to discern: shut up and remain silent unless permitted otherwise. You can see on her face that if such an occasion were to happen, she wouldn't be eager to punish you, yet she would do it regardless since she likely thinks it's her responsibility as your owner, in a similar manner on how you would punish an unruly puppy to train him to behave properly for his wellbeing as part of his new family and home...

The comparison is both somewhat amusing and denigrating at the same time, yet it's a fitting comparison; you're Shina's pet after all, and thus she's responsible for taking proper care of you, a responsibility that likely includes teaching you proper behavior.

Unlike a puppy, however, you're perfectly capable of understanding human speech, so unless you're so stubborn as to it be a detriment to your wellbeing here with the giantess...you only require this gentle warning to obey from now on that command. You nod in response, a gesture that makes Shina smile happily, now that's clear that you get the memo. It's after that she lets her internal muscles pull you back. 

You don't put any resistance, for it's pointless to do so right now, as well because if she is in the mood to have more fun later...you're going to have to take that nap she proposes.

And so, with the light from outside again being partially blocked by the girl's bra, and with you back inside her mammary gland, you crawl into the fetal position, and close your eyes, letting the warmth and the sounds of your place lull you to sleep. Yet as the darkness takes you again, you take the opportunity to make a key decision: the way you're going to interact with your "owner" for the time being.