I would say no because while in play means its ongoing. it wouldn't reactivate.
why wouldn't it reactivate? Each time Achan entered battle, his ability should activate and thus decreas Joshua by 5 more points.
The reasoning behind this is the wording. For example Death and Hades specifies to decrease the opponent's hand to 7 (or 9), but Achan simply says decrease by 5, much like that of a poison, disease, or other decrease ability cards like Job's Three Friends (whose ability activates every battle, if I'm not mistaken.)