
everything about isaac is just perfect for me PLEAZEEE I WANT MORE PRIESTS LOVE INTEREST PLEASE GIVE ME MORE OF THEM (i do not have a kink for priests. i am just tired of the dukes and crown princes being the male lead, please let me taste something new)
also because isaac looks and acts so much like romano from hetalia lmfao. i am pure cringe but i will never forget my love for romano so this is the best manhwa for me at the moment (unless anyone suggests another manhwa with brown hair, green eyed male leads who has a bad temper and etiquette but is a softie deep inside)

Alright, you challenged me to it, so let me see what I can dig up that meets some of your criteria. This is an assortment of non-standard MLs, to varying degrees of your required attitudes, with most focus on being nobility or adjacent without being a prince or a Duke.
Ascendance of a Bookworm (HIGHLY recommend the LNs)
The Lady Likes a Nerd over Princes
No More Princes (?)
I Woke Up as the Ugly Duckling
The Boomerang Duke (for his personality I swear)
Straight to the Red Carpet
On Her 94th Reincarnation, the Villainess became the Heroine
Madougushi Dahlia wa Utsumukanai (sort of maybe)
I’m the Villainess, so I’m Taming the Final Boss
The Villainess wants to Marry a Commoner
The Goddess of Healing
Primitive Boyfriend
Mahou Tsukai to Koi no Biyaku
My Ray of Hope
Tensei Shite Yandere Kouryaku Taishou Chara to Shujuu Kankei ni Natta Kekka

I try not to recommend things I don’t have a good opinion of. XD there’s only one that’s super weird, I think, and that’s Primitive Boyfriend. But it’s weirdly Otomege-adjacent and super non-standard ML so I went ahead and added it.
Ascendance of a Bookworm is one of your closest matches I think. Priest with bad attitude and manners as a main character for a good bulk of a 33 novel series. I love Ferdinand. He’s such a grumpy cat.

Though both of these are ones that start when they are children.
This one ml has like holy power
The Monster Duchess and Contract Princess
Surviving as an Illegitimate Princess-
This one her dad is a holy knight that doesn't acknowledge her because that means he broke his vow of celibacy.
This one he is kinda like a pope but also ruler of his own place
Daughter of the Emperor
This one I recommend the most has a type of priest only as a second ML, but the plot is different because main character is a siren.

after experiencing those second hand embarrassment of being rejected, i actually understand why FMC would just think that ML's approaches were platonic lmao
i mean, if i had the entire world conspiring against me when it comes to romance, i'll also just kill my desires for love and not assume stuff, even if it's something so obvious as the ML saying he wanna stay with me (still vague tbh, he could be saying it platonically /j)

after experiencing those second hand embarrassment of being rejected, i actually understand why FMC would just think that ML's approaches were platonic lmao
i mean, if i had the entire world conspiring against me when it comes to romance, i'll also just kill my desires for love and not assume stuff, even if it's something so obvious as the ML saying he wanna stay with me (still vague tbh, he could be saying it platonically /j)

dont get me wrong. i love arwin so much hes very cute. but i cant stop thinking about the crown prince who heard latte say "I dont fall for otherworldly beings"?? LIKE? PLEASE GIVE ME CLOSURE. just one extra route for him like with kenneth, please
aside from that, i love ibelin too? the idea of a protagonist being so loved, she never grew up from it because she always had things go her way. she never struggled and never had to lift a finger or two because the world bends her way. gosh, i need more moments where she just learns to live in the reality and have more latte x ibelin moments, if you get the gist of what im saying

everything in mangago is bad when it comes to this manhwa. which SUCKS cause the entire point of the manhwa is Nagyuun's internal dialogue when solving the dire situations
and the suspicions + foreshadowing end up becoming annoying too cause every hints were becoming shit. Like why the fuck are the Narins changing to Auchirdjjs something something? Why the fuck is Pitch Black Rooster changing to Black Chicken? Black Hen? What the fuck is everyone saying when their grammar sounds like it's placed in a google translate??
i ended up reading this in another site instead. at least the translations there were a lot better than the convuluted one we have here

I love dragon and his dynamic with our teasing Nagyuun. i love how Nagyuun looks so serious but is actually so childish too. and the fact that Nagyuun doesnt have a secret power that makes him... overpowered. nah. he's a tactician through and through and I enjoy more of his mind games solution than a brute force—but the author here definitely has the capability to show characters with brute force. *coughs in Pure White Elephant coughs*
even the annoying apprentices in the first few chapter ended up smoothing themselves in my heart like that Wardrin. gosh i can feel that crush he has on Luzian and it's adorable cause Luzian isnt your typical girl in a manhwa. shes a very straightforward but strong character. and everyone else is strong too
I guess my only annoyance here is how the povs sometimes break the tension of the moments? When Nagyuun is stuck on a situation and I wanna know what happens next, there are moments where we get the backstory of other characters that was just introduced and i ALWAYS get the urge to skim cause wtf I WANNA KNOW HOW NAGYUUN FIGURES IT OUT PLEASEEEEE
but rereading this again, those backstories were actually perfect. i just wished they werent paced in the middle of tense moments so i could appreciate it on my first read instead of the second lmao
trust me, i love men (IN REVERSE HAREMS!!! I REPEAT: IN REVERSE HAREMS!!) but didier's bobcut queen appearance? I MISS HER. WHAT HAPPENED. WHICH ONE IS THE TRUE FORM?? PLEASE