npcs in mhyk are a broad concept, so i will count as npc every character, that doesn't have a sprite, but is not mentioned regularly, like tiretta/alec. so, the first place is HWYLRYN. My baby. My sweetheart. My everything. fav chara screw you main cast. he is such a wonderful character, so deep and meaningful for the story, and i absolutely love the lesson he tought akira. (spoilers for 4th anni in the next sentence) i was VERY sad when he died, but it's also the only way that lesson could be tought and it was a beautiful and poignant finale for him. I love tou hwylryn i would do anything for you.
next is my "love" category, with isaac, eva, mia, and balthazar there. i think isaac doesn't really need any further explanation; bro changed the game for the whole fandom. he is cool character, i liked his storyline A LOT, and god i am WAITING for him to finally have a voice. eva is my bestie and good chara too. i like her story, her connection with Bradley, and the thoughts that she put in his head. rip queen i will never forget you. with mia everything is much the same, as with eva (i just like women that like bradley sjskjaj). i really like characters who're evil but not thoughtlessly cruel. her storyline was fire. i get you bestie, i would like to have bradley in a cage too ngl. also, a sexy woman with a WHIP as a magic object??? loud eating noises
balthazar is just. oh my god. i don't know where to start. FIRST this man perfectly reflect shymurr dillema, THEN he proceed to be gay as fuck for hwylryn, AFTER THAT my man became a pusher for caiowe, and AT THE END, he died with a big emotional impact after being pain in the ass for whole story. amazing. standing ovations. they will never make me hate you, balthazar. he is so complex, deep and fucking hilarious with his gay panic towards shylock and hwylryn. when shylock was explaining his feelings, which are THE SAME that's he has for murr i wanted to smash my head on asphalt ngl. but overall balthazar was also really important for the story; he pushed three whole pairings through it and owned every scene he was in. love you king.
I liked collins, vespa, tanya, dianne, claudia, muumuu (yes i'm counting him as a chara idc) and many others a lot! i wouldn't stop on them too much, since all this answer is getting too big already skjsksk.
as for the least favorite one i chose the villagers from east prelude and them only. i fucking hate every person out there, and they didn't deserve such an easy ending in the slightest.

that is some question! actually, caiowe was like love at first sight. when cain mentioned owen for the first time, telling about his eye, i was immediately like 🤭. now, i guess it's about their connection and how their fates are intertwined forever. cain is constantly pushing owen to new experiences and brings up from the depths of owen's subconscious everything that he tries to hide. while the whole point of owen's first encounter with cain is exactly the same, just in another wrap. also, they are hilarious, gay and scratch my brain in aaaall nice places. i want to see owen being absolutely terrified about waking up some feelings for cain and cain being straightforward himbo he is. also, their interaction while owen is in kizu state... chef kisses. i think what really made me as crazy about caiowe as i am now it's 1.5 anni. that was a hella ride