you have selected.... CHRONOCIDE
The lights of the summoning ring pulse and dance with the concentrated energy of the Saint Quartz she's fed in. Already, it's yielded to her a good half-dozen or more Craft Essences, occult items that they can apply to the Saint Graphs of her servants to boost them in various ways. It's even given her a second copy of a Saint Graph of David, strengthening the original.
But she's still looking for another Servant. Alongside Mash, and Cu Chulainn who'd followed her back from the ruins of Fuyuki, she'd managed to summon Heracles and David while in the middle of that hell. A good start, even if Heracles' mana requirements were a strain on her (and that was taking into account Chaldea's mana generators!).
Still. Where once there had been forty-eight Master candidates, only one remained. And she needs help if Chaldea is to truly stave off the incineration of humanity. Another circular burst of light - but it is another set of black keys. Then a bowl of mapo tofu. She sighs heavily. That's her reward from Fuyuki, gone already.
Mash, standing besides Ritsuka, gives a timid smile. The leftover energy from the circle skitters and arcs, dissipating into the air.
"There's always next time, senpai." Da Vinci, over by the computer banks and ensuring that the pattern at the heart of each essence is recorded correctly, hums in agreement.
[dialogue]
Then - the hum from the generators picks back up. Roman's voice cuts in over the intercom.
"Da Vinci - I thought only one summoning was the plan!" His voice is crackly with the surging energy.
"It was! The circle should have shut down!"
There's a shattering sound as the lights blow out - Ritsuka grabs Mashu and pulls them to the ground, turning their back on the overloading summon circle.

A hooded figure stands in the centre of the room, smoke rising around them.
"This is... unexpected." Their voice is muffled, but as they squat down next to the huddled forms of Mash and Ritsuka, it doesn't sound unkind. "My apologies for the damage, it was a little more difficult for me to answer your summons."
A washed-out cloak of what was probably once seafoam green conceals the bulk of their body, but gunmetal-blue shoes and off-white gloves are visible as she helps them to their feet.
"Call me... Brawler. That will do for now."
--
Roman lets himself into her workshop, two steaming mugs of coffee carefully held in one hand and a tablet under his arm.
"Well, Ritsuka-kun is taking Brawler on a tour, and Mash has gone with them to keep an eye on them." Da Vinci hums, and beckons distractedly. "What is it, what--" The data in front of his eyes makes no sense. He puts down the coffee and scrolls through it.
"You see? It shouldn't be possible." She's right. Brawler's Saint Graph looks nothing like the other Servants'. Instead of bearing a bronze, silver, or gold border, it's instead black. Attack parameters, skill stats - they're either unrecognisably corrupted or missing entirely. But... it feels familiar. Sort of.
Roman opens up the recorded statistics from when Mash was fused with a heroic spirit.
"There." He says, putting the two side by side. Da Vinci peers over his shoulder, watching as he points out the similarities.
"So Brawler isn't a true Servant at all, but a forced fusion between a human and a spirit." She takes a sip from her mug. "An unstable fusion." Roman frowns, shakes his head, stands up from where he'd been leaning on the table.
"That kind of thing shouldn't exist in the Throne. By rights, its very existence should have torn itself apart the minute the fusion finished." And Roman knew all too well what a failed human-Servant fusion looked like. Mash had been Chaldea's only success - and the blood price they'd paid to succeed was far too high to try again.