I think Least I Could Do has corrupted my mind beyond repair, and with that in mind I will give a cookie to whoever spots the paraphrased quote in this oneshot...
Disclaimer: Riichiro Inagaki and Yusuke Murata own the two main characters...
"Get off the swing, little baby! That's ours." A pre-pubescent male's voice ordered as Mamori was violently pushed off the swing she was using.
"Hey! You can't do that!" She complained, holding her scraped elbow with tearful eyes.
"Wanna bet?" He challenged her, his friends start laughing.
"I bet I can get your underwear so far up your ass it becomes your new anus lining." A calm, smooth voice stated behind the bullies. Mamori looked past them to see a boy with spiky black hair and a nonchalant expression.
"Oh, really?" The lead bully steppe up to him and pushed him back a few inches before laughing mockingly. "I bet you can't."
"Wanna bet?" The spiky haired boy grinned, displaying a set of teeth slightly sharper than normal before advancing on the bullies.
"Th-thank you… but you really didn't have to do that… erm…" Mamori stuttered, a bit flustered at what she had just seen happen.
"They had it coming to them." The boy shrugged, his narrow eyes averted from her and watching the three bullies writhe in pain desperately tying to get the back of their underwear uncaught from their zipper and back over their head where it belonged. He chuckled at his gruesome handy work.
"I… I didn't know that underwear could stretch that far…" she muttered in awe.
"I'm just good at what I do." He stated before walking off, headed for home.
"Wait, what's your name?!" Mamori called after the boy. He paused and glanced back at her.
"I'll tell you if I see you again." He said, raising his hand in farewell before starting to walk again.