Magic soap
Aurelius returned to the castle after a fruitful chat with the enthusiastic groundskeeper. His idea couldn't be accomplished in less than a year or two, so he "convinced" Hagrid to take on the project and help him.
He just had to stop by occasionally for tea and see how he was progressing. As for the rock cakes he carried with him, they could always be turned into deadly projectiles.
And speaking of deadly things, it would be Halloween at Hogwarts at the end of the month, and Quirrell would have released the troll in the castle.
'How about we put on a show? After all, there are many ways I could paint that situation. Make Dumbledore's incompetence shows with his suggestion that the Slytherins go towards where the troll is supposed to be? Point out that the golden trio did nothing wrong since they went to a place that should be safe to aid someone in following the headmaster's instructions quicky? Point out that our DADA teacher passed out to the rest of Britain to point out the inadequacies Quirrellmort forced Dumbledore to kick him out of Hogwarts? Now that I think about it, wouldn't Quirrell be fine with doing the DADA position since he's technically Voldemort, so the curse on the position is irrelevant? Meh, I'll play it based on how I feel at the moment. All of these are viable choices, and I have already given up on keeping the canon timeline.'
"Aurelius?" A voice took him out of his thoughts. "Why are you smiling as if you were a novel villain?"
"It's nothing, Silvia. I was thinking about the Halloween party," Aurelius answered when he recognized the person who approached him by his voice. "How is our soap project going?"
Silvia, a Muggle-born witch and first year Hufflepuff whom Aurelius bonded with during one of his Herbology classes when he saved her from being prickled into a human hedgehog. She was a little fuller, with glasses, shorter than even Aurelius, brown-eyed, lightly tanned skin, and her hair so white that it appeared silver cascading down to her waist.
She was particularly fond of anything that generally made life more pleasant and comfortable, with a happy but somewhat shy attitude. She only started acting confident after they met several times in the greenhouses.
"I have tried some combinations with the essential oil of the flowers and fruits you suggested, and the girls of my House gave it a thumbs up for its aroma and quality. We only need to give them the shape and the enchantments. After that, we can start selling them."
"Good job." Aurelius hoped she'd only need another week at most. "Prepare fifteen samples for me to examine and bring them with you when we meet after the charms lesson. After which we sign the papers, I'll give them the go-ahead, and I'll put the finishing touches on it."
"Gotcha! See you in two days," said an excited Silvia.
"Hmm, I should send a couple of samples home," Aurelius murmured as he walked away. "I think they'll like it a lot."
He jokingly mentioned an idea to create animated bars of soap with pleasant scents during one of his conversations with Silvia, and it just so happened that he learned how to make homemade soap as a child. After teaching Silvia his knowledge of plants, crafting skills, and some magic, Silvia successfully created a scented soap waiting to be charmed.
Now, all that remained was to shape them into adorable and harmless shapes like cats or mermaids, enchant them to keep their shape as they get smaller from wear and tear and help wash the skin. Once the product is finished, they will sell it for two sickles a bar. It may seem small, but the profit margin was huge.
The cost to create a bar of soap is only ten knuts, so they're selling it for almost five times the cost, and even if they split that profit, they'll still make more than double its cost in profit. If they sell one hundred bars of soap, that's already a little over eleven galleons.
The frequency of purchase of the soap, its variety, its convenient storage, the simple enchantments, its necessity...
Once the papers are submitted and approved and they get the patent, they can license the product, so it's pretty easy money. Eventually, they can automate the process or pay some people to do it.
Two days later, under the interested eye of Professor Flitwick, the soaps were transformed into simple but attractive shapes and enchanted with a simple combination of four basic charms, whose functions were animation, warming, self-cleansing, and moisturizing.
"A well thought out and safe application of charms," praised Flitwick as he took a closer look at the sample he was given in the form of an owl scented with wild berries. "Not nearly enough students apply what they've learned. Ten points to Hufflepuff and Galegold!"
Silvia and Aurelius exchanged glances and smiled.
"I would advise you give Professor McGonagall a sample as well, perhaps as a surprise."
"Don't worry, professor, we already thought about that." Silvia raised a vanilla-scented soap in the shape of a cat that moved from sleeping to standing up after being picked up. We were thinking of sending it by owl with a note to see her reaction discreetly from the tables of the Great Hall.
"Now I'm curious to see her reaction when she receives after picking up the bar," Flitwick said jokingly.
After Aurelius set aside three samples (two for his mothers and one for the magical patent office), Silvia took two more for herself and a friend. They signed and sent the relevant legal documents with Aurelius's owl. They should get a response the following day due to the simplicity of your product. "How do we use the remaining eight samples?" Silvia asked.
"Let's do a raffle so that two different people from Gryffindor, Hufflepuff, Slytherin, and Ravenclaw can get them," Aurelius suggested.
"And how do we do the draw?"
"Let's ask two questions, different for each house so they don't cheat, and the first two to answer correctly get the samples."
"I like it. Leave the questions to me; I have some ideas..."