Why do the Force ghosts tend to disappear when they're most needed and re-appear when they're least wanted? But there is a reason (and it's not lazy writing ;)) - Ben's test is not over in that cave and Rey has to see the whole extent of the Dark Side influence for herself.
Ben stays too long in that dark nexus and the dark nexus speaks to him about... many things.
"He who fights with monsters should look to it that he himself does not become a monster. And if you gaze long into an abyss, the abyss also gazes into you".
Friedrich Nietzsche, Beyond Good and Evil, Aphorism 146.
"What's in there?"
"Only what you take with you."
Master Yoda to young Luke.
Rey is under the impression millions of years have passed. The small camp fire crackles and starts dying out like a morning star. She grows impatient – but she already received a small slap on the wrist for being impetuous, so she gathers all her strength to remain still, legs crossed, with Kylo Ren's saber in a triangle between her and the Jedi spirits.
But then, something rattles and cracks inside the cavern. For a split second, it doesn't sound like a man-made sound. Then it subsides.
And then it's back again.
Rey tenses and looks at her Master. He seems almost equally worried.
Ben.
She jumps to her feet as his figure appears in the opening.
He is staggering. He looks tattered. He left that carnage on Coruscant almost unscathed, but now he looks like he was being tossed around and hit against the walls by a super-strong foe.
The look in his eyes terrifies her – it's downright deranged. There is no light of recognition in him. He probably had the same look after the Jedi temple was destroyed, but fortunately, has his mask then to cover it up.
Now, she is left alone with that barren landscape. The Masters are gone. Even the small camp fire before her dies to the embers.
Ben.
She swallows hard and makes one step forward.
But he doesn't answer. She might as well be yelling to a wall.
And then, his eyes fix on the inactive hilt. He almost has no eye-white in those eyes, that's how bloodied his gaze is and how dark his pupils appear.
The saber trembles.
"No", she utters as the despair penetrates her heart like a syringe. "No".
There are already tears in the edges of her eyes. But with her despair growing, so does her resolve – she will do whatever it takes, whatever it needs to be done.
The saber is the only weapon she has – she left the blaster in the ship (foolish girl, lowering guard so early and so eagerly).
She feels the tug. He wants that saber and the saber wants him. It is downright obscene, like a huge orgy unraveling in front of her unwilling eyes.
Rey has no other option but to activate the saber. It springs quickly and crackles in front of her face like a Dark Side beacon.
But as the Force hums between them, she has to try – once again, one last time.
Ben, please.
It almost feels like some kind of magic spell has been broken – he snaps out of his delirium and looks at her with shock and utter confusion.
And in the next moment, he is folded in half. Vomitting. Spasm after spasm going through his body.
"Ben", she screams and is at his side in only two jumps. Saber is inactivated and thrown away into the grass.
He tries to gesture to her not to come near, like a man poisoned or infected, but she is stubborn and disobedient.
Her hands lock on his shoulders and then pull his entangled hair up to the back of his head.
"It is alright", she whispers. "I'm here. It's alright. Let's get out of this place".