Yuuki has two Hypers, which will transform into each other depending on certain criteria.
Yuuki's main Hyper is Angel Hand. When used, the player will be prompted to target a non-KO'd unit. This can also target the player. Upon doing so, that unit will fully heal HP up to their maximum HP. The player gains 10 stars for each point of HP healed through this effect.
On all even-numbered chapters, this card will transform into Devil Hand.
Yuuki's secondary Hyper is Devil Hand. When used, one random non-KO'd unit will instantly have their current HP set to 1. This can also affect the player. The player gains 10 stars for each point of HP lost through this effect.
On all odd-numbered chapters, this card will transform into Angel Hand.
Angel Hand is a healing-based Hyper that can not only be used on opponents, but it can be used on the player as well. It is not recommended to use this card on others, as the benefit of gaining stars is usually not as impactful as the benefit of being able to survive by healing oneself. That being said, the card is an excellent star generation tool should a high HP character such asor present themselves in a scenario in which they are low HP. However, Angel Hand is expensive, and as such it shouldn't be used without care. Players should not only watch out how many stars they can get from healing a player, but they should also weigh if it would be better to use the Hyper on others, or themself.
Devil Hand is a disruption tool, and a HP-reduction tool. Being that it sets HP down to 1, this card can be an effective enabler towards getting an easy KO. Unfortunately, being that it is random, you can potentially miss your target, or you could even put yourself into a difficult situation by reducing your own HP. You are not likely to use this card for merely its star generation ability, but should you need stars, it is best to use it when most of the characters are either at high or full HP.