Reysol need first a good manager, because replacing Shimotaira hasn't worked well at all. They're gonna lose some players, but if they keep a couple - I'd suggest Segawa and possibly Koike -, they could go back with Nelsinho (rumoured to come back for 2019 season).
I hope Nakayama can moves to Europe, maybe Belgium/Portugal for a start. Its a pity that there are no European clubs interested in him. Reysol have quite a few players that I think other teams will be interested in like Nakamura, Nakayama and Koike, etc.