We still need more elaboration about why some flowerings are temporary, and others become permanent.
If I had to throw an idea out there I would imagine that the length of ones flowering has to do with prolonged emotional turmoil, we know that a flowering is triggered by some sort of traumatic event in the first place, but I think some commonalities between the seemingly temporary flowerings is that: 1.) the event that triggered the flowering was resolved by the powers of their flower and 2.) they didn't get the sorta "build up" period of enhanced physicality prior to flowering. Unless I'm forgetting a couple, the temporary flowerings we've seen so far have been Oscar, Zoe, and Lucas (up until recently) and all of their flowerings have been in response to the perceived deaths of people close to them and conversely all of their initial flowerings have neutralized the threats that caused them to flower in the first place: Oscar reversed Zahid's death and killed Kathryn, Zoe stopped Akira from killing Lucas, and Lucas stalled Akira and kept him and the facsimiles from killing his group. Since the event that caused their flowering in the first place was resolved I imagine they wouldn't be able to access that power again until another episode of extreme stress forces out the need for their flowers again.
As for permanent ones, it seems that their "inciting incident" persists for far longer. Miura for example probably began flowering in response to Lucas' mental decline as a soldier and being tipped over the edge after seeing Lucas put in a coma by the futurists, there was even the whole chapter of Miura watching Lucas go to music school and realizing that Lucas was meant for something more than just fighting and empathizing with him being repeatedly forced onto the battle field regardless. In Lucas' case I think that the cause for his newfound flowering isn't exactly Miura's death but the conviction to "destroy the world" that he gained because of it. In both Miura and Lucas' cases the goal of their flowerings aren't immediately resolvable simply by flowering ("Insuring a better future for Lucas", and "reshaping a war torn world" respectively) but the power of their flowers are necessary stepping stones on the path to their goals and my prediction is that once Lucas achieves his he will lose the power of his flower and the same for Miura had he survived.
Conversely, I predict Kayano will lose the power of her flower once she finds something she wants to live for outside of being a soldier. We still don't know what happened in her past to cause her to flower in the first place, but she was presumably groomed from birth into being the perfect soldier for the empire, so I would posit that her entire life up to this point has been one big traumatic flower-inducing event, and once she moves past it and finds something to be genuinely passionate about she'll lose the powers that stemmed from her past.
