fun idea! shadow starts to die slowly no one, even himself, even notices it at first but he starts getting weaker and his mind starts getting foggier and he realizes that the only way he can actually use chaos energy as usual or even function normally is if he has off one inhibitor ring he has a harder time using chaos energy and its even more painful than before, any chaos emerald he uses barely does anything either
sonics the first to notice he realizes shadow starts wearing baggy shirts in the summer he tries asking about it and gets brushed off and when shadow turns away he grabs his wrist- and freezes. theres no inhibitor ring a week or so later shadow explains
theyre in the middle of battle and shadow looks terrible, even though before hes been fine at this same point in previous battles sonics the only one who sees him take off the second inhibitor ring and shove it in his quills he doesnt tell shadow to put it back on after
sonic and shadow are watching a shitty show they started watching together and after a big plot twist sonic turns to shadow to gossip and theorize hes dead asleep softly snoring shadow has never fallen asleep somewhere aside from his desk or bed hes never fallen asleep in such a vulnerable way or place sonic calls rouge
a while after that sonic goes to shadows lab (it used to be geralds, its now shadows) shadows sitting at a desk and willingly invites sonic over he thought hed have to convince shadow to let him stay shadow says he found out why hes losing energy
his black arms dna, after dooms return and the awakening of his doom powers, is taking over the rest of him including his chaos energy and if his doom energy takes over the chaos energy, it will kill him its been killing him when the black arms dna and chaos energy fully takes over one of two things will happen
shadow becomes fully black arms. no thinking for himself. no individuality. only doing what black doom tells him to.
he dies. simple as that. the immortal shadow the hedgehog gets killed by the thing that gave him life
by the time he fully figures out whats happening he has a few months at most 2 weeks at least
shadow gives sonic a doom spear incase he turns into a black arms someones gonna have to kill him