Shodai Nekketsu Kouha Kunio-kun/Ki powers

Ki (キリュク) is used to power magic-like effects, and is functionally comparable to mana. All restorative effects are permanent but boost effects are purely temporary and will run out very quickly. Ki fully restores when you sleep in your bed (and partially restores when using the Sleep Ki) so if you know you are going to return home soon you might as well use it up to make things easier.