Nanako just need to find her thing to shine, already has determination but a right push to a direction should be enough...
As
@Jeirien mentioned, common trope is a "grown up" mentality being in a younger body might be effected by completely different set of hormones and brain activity of a body.
Think I have only read one novel where +40yo mind replaced with a 3yo, he immediately noticed something is off, plenty of things starting from libido to acting like a child in unexpected situations where an adult would behave differently and only after calmly calculating the situation he was at, came to different conclusions. But still, here we have a 18yo with at least 3/4 of body development...
Thanks for the scanlation!