Headcanon: Yuji broke his binding vow with Sukuna
To start this off, we have no clue what happens when you break a binding vow with another person so I am going off the assumption that the person who you broke the binding vow against gets all the benefits from the vow and you get only the downsides.
Since Yuji did not know about this binding vow and therefore could not fulfill it, Sukuna could gain control during that period and hurt absolutely anyone he wanted, but of course he did not know this because it's stated that nobody knows what happens when you break a binding vow with somebody else and just played it safe. This is why Sukuna could hurt Hannah and Yuji.
My guess is that Yuji did include himself in the binding vow naturally, but since he did not uphold his end by willingly giving up said control Sukuna just got it anyways, letting him knock out Hannah and cut off Yuji's finger and forcefully feed it to Megumi.
