Harry Potter went plummeting down the stairs, nearly down to the dungeons when he heard Blaise's voice. He whirled, and headed out towards one of the first year courtyards. There! Harry lunged, grabbing Blaise neatly by the back of the robe, apologizing to the girls he was sitting with, "Excuse me, urgent business." Harry didn't notice nor care about the girls' sudden excited whispers. Later he'd realize that he was the reason for Blaise's persistent "he's gay" rumor. *
Inside a classroom, Harry slammed the door, and then cast a Petrificus Totalis on Blaise, who blinked at him. Amending his plan, Harry cast a silencing charm, and then a notice-me-not - it wasn't the best he could do, but he didn't want to set off SnapeRadar in case the dour bastard was lurking in the corridors.
"Do you remember our bargain?" Harry Potter said. Blaise blinked in acknowledgement. "I'm amending it, now."
Harry had raised his wand to Blaise's temple, and the dark skinned boy kept trying to twitch away.
"Think hard about our bargain," Harry Potter said, "I wouldn't want to remove anything else."
Blaise's dark eyes had gone wide at that. Oh, so so wide.
Harry took a deep breath, muttered, "Obliviate" and dove in. Blaise's mind was a mixture of Quiddich mud and mangled house design. It was difficult to find anything - but Harry could see the open folder, and he quickly traveled to it, in the way that dreams let you. Standing there, he struck quickly and mercilessly, burning the folder and its contents.
Harry took the memory that he'd crafted, and inserted it subtlely and slowly, letting it take root, as Harry spent the half an hour required to make the false memory charm stick.
*Harry doesn't get one of those because the girls would rather fantasize about him. For now.
[a/n: Leave review? Didja want more description of the spellcasting?]