Cicada's Dagger is Metatech Shrapnel
We had theorized that Cicada was merely a passenger to his dagger, the true villain and unknown power of the season, but the introduction of Metatech - the notion that things, and not just people could be transformed the way humans had been in the past - has sealed our suspicions. For starters, to call it a "dagger" or "knife" seems to be misleading, since the evidence suggests its Flash-like insignia is a total coincidence. And that it was never meant to be a knife, either. Merely a piece of Metatech shrapnel launched away from the satellite explosion... and embedding directly into Cicada's chest.
Of all the glimpses into Cicada's life, the shot of him revealing his own chest wound to his daughter's doctor seems the most important. The wound itself looks like a serious one, so Sherlocque's deduction that Cicada's lung injury causes his fluttering breaths makes sense. But the nature of the wound is most telling: glowing with yellow energy, not unlike the jagged piece of metal which glows on a similar way - when craving Metahuman energy to be sated.
How the dark matter-charged metal shard flung itself into Cicada's chest is a simple enough mystery to solve. Either shrapnel from the satellite, or metal from his factory job was imbued with dark matter energy the same as other Metatech. When it struck Cicada, the wound itself doesn't seem to have put his life in continuous danger. No, that's the glowing mark of Metatech, which makes his crusade against other Metahumans seem somewhat straightforward, right?
Cicada Needs To Feed The Dagger Meta Energy
If The Flash's showrunners have introduced Metatech, and implied that the nature of metahuman powers can now be applied to objects, then the simplest explanation may be the correct one. Cicada (not his actual name) is struck by metahuman energy thanks to another dark matter, dimensional-smashing storm related to The Flash and S.T.A.R. Labs. With a dark matter affliction that seems to be killing him, Cicada begins hunting down other metas, killing them, and somehow absorbing their own metahuman energy to keep himself from succumbing to the affliction (and a nasty wound) so that he can stay alive for his sick child. That's anything but an original character arc by this point, as several Flash villains have suffered from accelerated aging, nuclear instability, or other metahuman curses that seem to be treated only by killing/absorbing/negating other metahuman gifts.
However, add the twist that it's actually the knife in the man's hand which seems to be what's killing him, and killing metahumans to be kept at bay, and the same old story no longer makes sense. Unless, of course, you introduce the concept that the 'knife' actually fills the role of the metahuman energy in this scenario, both killing and sustaining Cicada. If it seems that simple, there's no need to dig any deeper until we get evidence to the contrary.
The only real question now is: with Cicada's symbiotic bond to the metatech/dark matter shrapnel/dagger clearly destroying him, how will the the team actually help? To tackle that conundrum, we'll need to see if our theory is accurate first.
The Flash airs Tuesdays @8pm on The CW.