MC is aware that Arina loves him dearly and since they grew up as children, he only knows her weak and demure side. Also there was an event in her past which she almost lost her life due to bullying and he was unable to save her, and he swore never to allow that ever to happen again to her. He wants her to become independent of him and encourages her growth. As such he is not aware of her dark side. No he has absolutely no clue of her yandere side, if he knew he would probably run like hell, but alas he has no chance in hell of ever escaping her.

The c*ckblock is strong in this story, but really worth it in the end. I will repeat, Arina is YANDERE of the YANDERE. she puts all previous yandere to shame. Ye have been warned, laughing is not allowed or she will strangle you thru the monitor, that is how strong her yandere is..............

She protects the girls the MC likes and adds them to his harem (some of it is really messed up how she does it lol). There is ZERO chance of NTR.

Our main character, Yuuki, isn’t useless but he’s only just ‘above average’ - aka nothing special. He’s a caring guy who’s gotten used to being pretty-much a carer for his childhood friend, Arina, who happens to also be the hero. Over their summer break from school, she’s destined (conveniently, I’ll add) to travel to another world of magic and swords to “slay the demon king” ya da ya da blah blah (it’s a bit like that for them too as this entire sequence of events is enacted almost frivolously). Yuuki is invited to come along with Arina and eventually consents out of concern for his dear childhood friend whom he believes will absolutely die the moment he takes his eyes off of her - and just forget about her “slaying anything”.... Unbeknownst to Yuuki, Arina is in fact extraordinary, especially in a single, specific field: worshipping Yuuki. Arina intentionally derails every plan for a regular journey whenever she gets the chance, all for her carefully-considered schemes to thrust the world and all that it knows-and-possesses before Yuuki’s grasp. Every interaction, every step, all good and ill will, every gift and every consequence, and most of all, every friend, acquaintance, enemy, and love-prospect, gets filtered, adjusted, manipulated, and dominated before it can even hope to catch a glimpse of just Yuuki’s shadow—but Yuuki knows not of this. After all: “...A-A-Arina is s*upid and hopeless! S-s-s-sorry, Yuuki, please step on Arina! A-Arina must be punished!”. With a mask of a childhood friend untoward Yuuki, and the visage of a demon unto all others less fortunate, the story of two friends gripped and bound by a shared trauma, as they venture into a world that’s unprepared for what is about to be unleashed upon them.

Those... I guess poor bandits, they know not their misfortune when they tried to think of laying a hand on Arina's chastity, which belongs soley to Yuuki, and the so called "men" that dared to touch his property should receive their punishment.... a violent and brutal death, which includes to their Johnson. And yes folks, you read right., she identifies herself as his property... not sure how that works out exactly but okay.

On that note, brainwashing, corruption, mind control and such all seem to come into play. That Princess Rose that they met? Yea Arina did something to her, and know she seems to totally love Yuuki now, being a woman with zero experience with boys or men in general, I guess she just didn't know what to think, but when she got left alone for a bit to think about her odd behaviors her logic just somehow looped from thinking he was suspicious, to a nice man who was well educated and just found herself thinking.... "what was suspicious?" Later we find that she used sci-fi like nano machines to do that to her, though she also makes use of upgraded slug things that she repurposes

She also apparently wants Yuuki to have more children than he can possibly provide for him herself...

Major spoiler for Arc #1 did Arina know about that "forbidden bracelet" ? is everything according to her plans? I really really hope so, I worry about the protagonist and those he loves after that. Now for some major story spoilers for the second arc. Oh my gosh! Time traveler enemy!? I did NOT expect that, but even with that being said, I really hope Arina manages to either +1 to the harem or destroy her, as for what will happen... unfortunately with serious implications going on, extreme cliffhanger between chapters 54 and 55.

so this is to help you before you read there is one main yandere she is extremely manipulative and the women that MC helps, or takes a liking to makes them into Yanderes... also about the whole masochist thing that trait belongs to our females not the MC. Oh ya MC has no clue that Arina being completely over powered. Also on a side note Arisa has a hidden past which we aren't clear about besides MC takes care of her and has failed to help her once. Well that's all I can give you...

Current Confirmed Harem Count : 3 -Arina- time traveler, Yandere, masochist, cold blooded, childhood friend, Hero, and ? (she has a lot unknown about her) ;Rose-princess, was "changed" by Arina, oh and also a yandere (sort of,.... blame Arina;and Mist-who was a maid in a terrible house (you'll see), again she was also "changed" Arina,.. well she is a yandere (I think) without Arinas help... or she just really really liked Yuuki.... Well she's also a Yandere.

Oh ya also if you want to know who becomes the demon queen/king it is the nun who was r*ped, violated, and abused by Gellen. Also if you were worried the story hasn't had any of the heroines r*ped... The story has Arina the yandere hero who is OP who basically protects the harem because the MC would feel sad without them....

Well ya that's about it without revealing the story so injoy it gilt free :)
Oh also Arina is scary.

p.s, the hero Arina is a crazy yandere behind yuuki's back, but a meek maso in front of him. And pretty much yuuki is o blame for her 'irregularities'. How you ask? Just read then.. It's fun. And the way the first boss died is funny. At least to me.