Injury and Healing
Injury
One ability common to most Mahou Shoujo characters, regardless of theme, is the ability to take more damage than a normal person would and come out still able to fight. From walking through fire to being flung through buildings, the characters this theme is based around handle things far better than your average teenager! And while they may get bruises, scrapes, and cuts - those tend to heal quickly and without issue.
That doesn't mean that more severe injuries aren't possible. From being attacked by a truly overpowering opponent to an unlucky situation, it's possible for a character to take a more severe injury - something like a broken bone or severe burn, or even more life-threatening injuries. However, since the recipient is in charge of describing how much damage they take, don't take serious, specific injuries like broken bones or similar trauma, unless you intend to sell them for at least a short time, even if you have access to magical healing - being the recipient of such damage only has any dramatic value if it sticks a little bit.
Healing
As stated above, all Mahou characters (anyone with access to magic, whether via a henshin or Dark Energy) heal quickly, and in general combat wounds that aren't being used for dramatic reasons shouldn't be present beyond that day or so.
When it comes to more severe trauma, they heal faster as well - and may have access to magical healing from characters who have the ability to heal others in their powersets. Access to magical healing from another player can drastically shorten but not eliminate entirely the time to recover from serious injury, but the impact of this is known to vary from person to person, from situation to situation, as magic is affected by many unknown variables including emotional states, and is at the absolute discretion of the person healed. Players can determine for themselves whether healing any particular injury leaves a scar or not, but are discouraged from having a large number as it kind of goes against the bishoujo aesthetic.
While magical healing is possible, there is no such thing as an 'instant' heal other, that would be functionally an in-combat heal - such as a 'Cure/Cura/Curaga' type spell or an RPG Healing Potion/Phoenix Down outside of major and important events (this means cleared with Staff prior.) This limitation doesn't apply to characters who have a powerset or abilities based around healing themselves only in combat (see below).
Exceptions
Characters who have the ability self heal only, as a major part of their powerset, can play more loosely with the damage and healing rules as pertains to themselves. In this case, occasionally taking severe damage only to rejuvenate it instantly is an artifact of their powerset. This ability tends to be rarer among heroic types, but an example CC would be Sayaka Miki. They're still advised to mind the rating of the series and avoid gratuitous gore, as well as taking severe injuries for no narrative value.
