6.7Next destination: C major

Now:

D♭maj7 → Dm7♭5 → G7 → Cmaj7

The last three chords are:

Dm7♭5 → G7 → Cmaj7

At first glance, Dm7♭5 is not the normal ii chord of C major.

Normal ii in C is Dm7.

So what is happening?