Curate, connect, and discover
I lied I wasn't done with this idea so have a highly edited version of my vision
Senku and his mildly crazy partner
Everyone thought that Senku, Taiju, and Yuzuriha were a trio.
Until Taiju comes running one day during the building of the Perseus, a statue held over his head, screaming from the top of his lungs
"Senku!!!! Look!!!! Look who I just found!!!!"
No one has seen Senku drop everything he's doing that quickly before.
That's how the kingdom of science finds out that the trio is actually a foursome. A quartet.
That's also how the kingdom of science finds out that the reason Senku seems so adverse to romantic relationships is because he's already in one.
They adapt to the stone world quickly, though they stick pretty close to Senku throughout the day
They don't appear to be the jealous type, getting along easily with Ruri, and seeming to pay no mind to any other girls who may be a little too sweet on Senku
But sooner or later, the truth comes out
Senku's partner is more than a little unhinged
They are the reason Senku knows what chemicals can be used to effectively melt corpses
Among several other concerning things
It becomes clear that their usual pleasantness can (and will) be dropped at the snap of a finger
Their usually pleasant smile will twist into a more sinister one when they get angry, though their voice may remain calm and light
They'll tear someone apart verbally first, but if that doesn't work, well, just pray there isn't anything they can hit you with
(There is always something they can hit you with, even if it means Senku loses dangerous chemicals out of the lab.)
Senku is fully aware of everything they can/have/will do, and openly thinks it's hot
When compared to Stanley, their response is simply:
"Nah, I'd win. He has more morals than I do."