The 'b' sound is a plosive too, by the way. It's voiced, vs the voiceless 'k'.

But the place of articulation kinda flips, from rear consonant/front vowel (kiki), to front consonant/rear vowel (bouba).

If you flipped the voicing, it'd be 'gigi' vs 'poupa', which to my ears at least, is a lot less clear cut.