At this point, I am pretty sure they are, especially Dane and Grayson. Dane being a former boss (in the military I think?) of Josh and Grayson being Chase' older brother (who basically unintentionally but STILL caused Chase his trauma). Excited to see these two's appearance in this art style. (I also hope Zig-nim releases their novel as soon as she can coz I feel like I might end up my 40's before that happens lol)
Grayson for SURE will appear he practically the main villain of KMIYC lol... sorta. They cut so much of chase out of KML so I'm worry if the manwha will be faithful to the original KMIYC novel and keep everything in Including all the character appearances.
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I wonder if will get to see Dane, Yeonwoo, Grayson, & Keith in this new art style caues it a million times better than the character design from KML plus all these characters did appear in Josh x Chase Novel & they weren't cameo appearances.