It dosen't stop her from stepping on Tenshi though.
The intent isn't to protect Tenshi - it's to protect Yuuka's hands.
Updated
Here's a charm.
Trainer
Yuuka, are you hitting someone at high school?Eh!?My classmate told me.That's me.Is that her little sister?I'm an only child.My little sister did this yesterday so I wouldn't injure my hand...Why've you got a bandage wrapped around your fist?Is your kid sister a trainer?