I was thinking, it's possible to plot inverse an animation??
Clear["Global`*"]
k = 0.002;a = 0.68;
1/Sqrt[k] x Hypergeometric2F1[1/2, 1/(2 - 3 b),
1 + 1/(2 - 3 b), -((x^(2 - 3 b) a)/k)] /. b -> 1
animation = Animate[Plot[1/Sqrt[k] x Hypergeometric2F1[1/2, 1/(2 - 3 b),
1 + 1/(2 - 3 b), -((x^(2 - 3 b) a)/k)] Sqrt[1 + (x^(2 - 3 b) a)/k], {x, 1, 100}], {b, 1, 2}]
AnimationDirection -> Backward
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