like the beginning of onimai is really good because you see mihari being calculated right off the bat. In a lot of genderbend manga, you see the MC explore their new body... to various degrees. But here, Mihari interrupts this process. She examines Mahiro's new body before she gets a chance to herself, then quickly heads off one of the main factors which kept mahiro shut-in previously.
Not only does this further Mahiro needing to find new constructive activities to fill her time, it also majorly effects her lived experience in this new body. Before the change, we know Mahiro spent much of her time playing video games or consuming pornography. This would've bred a separation from her body, making it something she only interacted with as an interface with her computer or to produce pleasure through masturbation.
But now, Mahiro is in a new body. It's a young girl's body. From what we know of Mahiro from later chapters, it very well may be the kind of body she often saw in her porn. At this early stage of inhabiting her new body, Mahiro could easily fall back into old ways: sit at her desk, stare at a computer screen, and forget her body exists except for hands on a keyboard and whatever she sees when she's jerking off.
But! Mihari blocks that. This accomplishes two things: as previously stated, it blocks one of the main ways Mahiro occupies herself while shut in, and it makes room for Mahiro to start seeing/experiencing her body as something new. And this does start to happen! In the very next chapter:
Mihari gives Mahiro new girl clothes to try on, and Mahiro is genuinely happy seeing herself dressed up that way!!
