Saying 'I have proof I have magic powers' would be pretty alarming in this context.

In hindsight, shoving his upper arm into his throat with no preamble, and then trying to say "I think I actually have magic powers" around it is more alarming.

"Wen Ning! Get that right out of your mouth this instant!"

... That's probably a rational response.

He does so.

"How is your throat? Is it bleeding?"

"It's fine. I, uh, can apparently do that now?"

"...Let me see it again."

Behold: he can fit an arbitrary amount arm in his mouth.

This is only not the most awkward experience in his life because of his skill at making things awkward.

"...that is not in fact physically possible."

And arm back out of mouth.

"I thought so too. --I c-could be a wizard and psychotic."

"I didn't think you were psychotic before, I have no reason to believe you're psychotic now. I've seen many psychotic people in my emergency room and you don't have any of the signs I'd expect. And you have magic powers. --Why did it decide to teach you the spell to put your arm down your throat first."

Great question! Not one he wants to answer for his older sister! 

"It gave me a more resilient body generally? That was just the easiest one I could test."

"What else can you do? What do you know about magic?"

"N-not much?" Which neatly answers both questions. "I'm more mentally resilient as well as physically, and my third spell is basically 'you are magical.' As is my one boon, which is separate from spells in a way I'm not clear on. If I do quests given to me by the thing that gave me magic, I can earn more boons? I could chose to become a shapeshifter or have limited telepathy or things like that. Also I have stats now, but I think the magical thing is that I know them objectively, not that I have them?"

"And it happened to you because you... took an oath to spread joy in the world? And that gave you magic powers?"

"It offered the oath, and I accepted it, yes. Also for some reason it chose me as the only wizard?"

"I want magic powers! Tell it to give me magic powers."

Quest available: No Greater Love Than This

Enable Wen Qing to be the second wizard on Earth.

Success: 10,000 xp; Wizard Alone perk.
Failure: Decreased relations with Wen Qing. 
Accept Y/N?

He is eventually going to stop startling when those purple boxes appear. Goodness that's a lot XP.

And also a very bad failure state.

"There is a boon for that I can take when I earn one? ... also I just got a quest that implies I can do that without the perk, but it's vague on the... how..."

"I guess maybe they want you to figure it out? Don't worry, I'll help you."

"It's worth a lot, so that's probably what's going on..."

He is helping his sister become a sex wizard. This is how his morning is going.

It is a bad idea, but he accepts the quest.

"I don't think swearing the oath would be enough, but it can't hurt?"

"What do I have to say?"

In Love's name and for Love's sake, I assert that I will employ the Art which is its gift in Love's service alone, rejecting all other usages.

I will spread joy and ease pain. I will fight to preserve what loves and rejoices well in its own way, and I will change no object or creature unless its joy and love, or that of the system of which it is part, are threatened.

To these ends, in the practice of my Art, I will put aside despair for hope, and hatred for love, when it is right to do so-- Until Universe's end.

Thank you, useful but startling purple screen.

He reads it out slowly, giving Wen Qing a chance to follow along.

Nothing happens.

"Well, it was worth a try. So what does it want you to do?"