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.