What the heck is that Serika doing? Her rank is bloody 2.5 times higher than Soluse's. Is she actually hiding her true strength from her own team, even to the point of watching them die, despite being able to save them if she wanted to? With her rank, this dragon shouldn't be much of a problem for her. Hikaru was indeed wise not to approach her, despite the possible Japanese origin. If Serika would rather lose her friends than expose her true power to the folks present, then she's definitely not trustworthy.
Sure, she has a truckload of unused soul points, which might suggest she hasn't got the soul board power like the MC, but her rank is 104! She wouldn't have achieved such an exceedingly high rank without killing masses of tough opponents. So, she definutely has a whole lot of power she's not putting to use here. Like I said earlier, it's quite possible she's actually saving those soul points for some miracle skill that requires 30 or more points to unlock, at once.