Despite how repeatedly Reimu told everyone who visited that the hakurei shrine was, as the name suggests, not some type of festival space, parties continued to happen on the regular. And it was at one of these parties, surrounded by familiar faces of friends and (former) enemies, that a particularly drunk Suika decided, in her mischievous stupor, to let Reimu experience a common prank of sorts under Oni: A simple scare using manipulation of mana, where the victim, too distracted to pay attention to their mana, would have their own pool overloaded, causing them to 'explode' into a puff of smoke, the cloud fading to reveal them covered in soot.
And so, she waltzed over to the shrine maiden, currently loudly conversing with her good friend Marisa about the process of youkai extermination, much to the uncomforting of the many Youkai present, and awkwardly tapped her on the shoulder. She attempted to say something to grab her attention, only pouring out some indecipherable slur of words. Reimu turned around and stared at the Oni, who thinking how the trick she had done thousands of times in her life went, with a combination of vague intrigue and irritation. After a moment, Suika held out her hand with a faintly understandable grumble of "grab my hand" while attempting a soft smile. Reimu calmly accepted the request; a single eyebrow raised all the while. With no more physical barrier between the two, Suika started manipulating her mana into moving towards Reimu's pool.
She first noticed something was off when the process seemed to be taking a few moments longer than it should, but shrugged it off as a trick of her intoxication and kept going. As she could feel the end approaching, she suddenly noticed Reimu, prompted by Suika's lack of further action, was only moments away from realizing what was occurring. She quickly decided a distraction was necessary.
"Hey, Reimu."
"Yeah?"
"I love you. Do you wanna go on a date?"
Watching Reimu's facial expression made it clear to Suika that the attempt had worked flawlessly, and she was already howling with laughter on the inside at how beautifully this joke would unfold, Reimu's current stare of complete bewilderment turning into one of scorn while in a smoke cloud. "Who cares if it's taking longer than usual, she probably just has a bigger pool from all her Miko work. It'll surely lead to a bigger boom anyway, which would be its own reward for tricking the one and only Hakurei shrine maiden." Would loosely paraphrase Suika's thoughts during these last few moments, completely missing the fact that Reimu Hakurei was, despite all of her grand achievements, only a human and, despite all of her magical abilities, still had the body of one.
What followed was a certainly above-average explosion for what this prank usually entailed. In fact, it momentarily overwhelmed the already broadly smiling Suika, giddy to see her successful work in all its glory, and also her senses, her eyes instinctively having closed from being hit by the blast.
In the moments after, she moved her free hand to her face intending to wipe away the dust and debris of the explosion from her eyes. After all, what a good prank be without being able to see the victim's reaction? Her expectation of dry powder, however, contrasted with her actual taction, which was of a sticky liquid.
Suika paused. She slowly and composedly moved her hand back and opened her eyes.
Blood covered her fingertips.
She brought over her other hand, still holding Reimu's, only to see that, as it came into view and the dust and smoke around her settled, what she was holding onto stopped existing beyond the wrist.
Her drunkenness disappeared in an instant, and her hair stood on her neck as she stared at the detached hand. A flurry of emotions engulfed her while she felt sick to her stomach beyond what she had felt in centuries. She could do nothing but stand and stare as more and more of her surroundings were revealed to her:
Everyone and everything in a small radius around where Reimu had been standing was covered in a mixture of dust and blood. Random bits of flesh and the ends of her extremities littered the ground. Complete silence enveloped the area for a seemingly endless moment before a cacophony of screaming and howling began.
Suika, unable to bear everyone else's pained faces and sounds, turned her attention towards the now red ground, collapsing onto her limbs and attempting to cover the wails of agony with her own. She was spared from having to continue wallowing in her guilt by Marisa, who, in a moment of emotionally overwhelmed vigilantism, used her freshly taught knowledge to swiftly end Suika's existence.