Those who say Chibi designs are out of place and "ruin" the flow are just talking out of their ass.
So tell me, did this frame of Chibi Tanjiro
Ruin the seriousness of Gyutaro's backstory ?
No it didn't.
Does Miki's tomfoolery in one episode
Make Parasyte anyless Gruesome ?
No it doesn't.
Does Gojo and Geto being goofy
Ruin Riko's death ?
No it doesn't.
Chibi moments give a break from the seriousness not ruin it. It also adds more human side to the characters instead of making it feel like they have a stick up their ass the entire time.