Nobody ever asks Tobi what he fears the most.
Living with the Akatsuki in that massive cave, it takes every ounce of strength he has not to scream out in horror every waking moment. Being surrounded by stone, suffocated by it—he gets fleeting images of rocks piling (deafening) up above him, blotting out the sun bit by bit, as raw, rusty agony screams across his right half…and the rocks keep raining down and down and down.
The phantom pains keep him up at night. During the day he can ignore them; he can concentrate on getting Deidara-senpai to like him, on being an acceptable member of Akatsuki. At night, though, he can still feel the anguish, acute at first (he feels the bones crushing slowly under the inexorable press of the boulder) then followed by the even more frightening creeping numbness (death can't be far). His mechanical hand flexes involuntarily at times like this, tightening in the bed-sheets as if in rigor mortis.
It's heavy, this alien half; it has taken him over a decade to get used to the uneven weight of his body, to relearn basic motor skills (to walk), to hone himself back into some semblance of a ninja. This is part of the reason he is so proud, now, to be a part of Akatsuki; he has come a long way from that evening on Orochimaru and Sasori's operating table, come a long way from their impassive faces and murmured commentary as they stitched him and wrought him back into a parody of a human being. He is deadly now, perfect as a patchwork monster can be.
He had a soul once, he supposes. He meant something to someone, once long ago.
He gets headaches when he thinks of it too hard. The best he can ever hope for are the fleeting images (glimpse of blinding sunlight through the canopy) of a boy with silver hair and a caustic tongue, a lazy-looking glance that makes him feel (Angry? Jubilant? Hurt?),
It flits away as soon as it arrives; his brain stumbling on the first—or is it second?—syllable. Ka—ka—ka—ka—ka—ka—
Tobi is afraid of the stone. He is afraid of his memories. He is afraid of himself. When he braves the mirror (not often), he sees a ruined face, a single eye, just like Itachi-san's, looking back. Red ringed in black ringed in red studded with black. He sees the future, somehow…
Somehow…
He sees things he shouldn't, when he sleeps. More fractured images—a village in the trees, nestled under a cliff-face—a surly little boy who could be the spitting image of Itachi-san—pages of some smutty novel—a fox-faced child with frightening power—the reflection (his?) in the mirror, of a sad and weary silver-haired young man.
He doesn't know what to make of it, as he shivers in his sleep, surrounded by stone, bathed in wan moonlight from the tiny aperture he has blasted in the wall to keep himself sane. He doesn't know, and it hurts too much to think about.
He lives quietly with his fear instead.