Looking for interesting isekai idea to write (Male MC)

Protagonist is a failed boy who didn't manage to get into uni, he's disowned by his adopted family and goes around lifelessly with no aim but some time later he wakes up being summoned by an ancient demon as a last resort to save the demonic capital from ruins. Now in this world there's the demonic empire who have been under peace for sometime however they hear about 4 heroines being summoned respectively as warrior/martial artist/archer or magic riflesman/healer with their magic elements being ofc fire/water/holy/wind/earth/grass (you can choose which elements they have, maybe all of them have all the elements if you want). They're respectively summon from the Royal Capital as the heroines of the countries of elf / beastmen / humans / spirits who all worship a goddess each. They'll be able to talk freely to theiir goddess like in the novel Goddess with zero believers however they hold a seperate identity which is the Protagonist's sadistic elder sister who incented her parents to kick the protagonist out and her friends each very beautiful and charming known for their different personality sadistic and forceful/cold and mature/popular but prideful/quiet and calculative. For the fun of it lets say they go on journeys and fall in love with each other (yuri love harem ig?) however the protagonist stays a loner and is determined, whilst the "heroines" advdenture for 2 years or so the Protagonist trains in dangerous martial arts, works out his physical body to the point where he does pressups with the weight of a mountain on his back, becomes adept in any weapon and assassination, cries out tears of blood and determination whilst his mental will becomes stronger and trains his "odd magic elements" which no one else has which are space control/darkness/dark healing (same as holy healing but with darkness effects instesd so like Holy regeneration would be Darkness Regeneration)/anti magic (woohoo tributes to Asta, which he can use for a certain amount of time lets say 5 minutes with 2 minute cooldown) he also doesnt stick to a specific weapon but mainly uses his insane martial arts and takes weapons of opponents and uses them if he wants or needs to. Protagonist's love interests now, he has the ability to talk to the goddesses in his dreams and at first they hate him but develop interest and to change it up a little lets say the Protagonist always wears a mask, has an average face and his elder sister n friends have no idea its him that they're meant to defeat and have occasionally met as adventurers (yeah he becomes one after he comes out of training) and he has even saved them before but eventually due to the guidance of theiir goddesses they suspect and attackk him, he doesnt attack back because he knows he'll kill them due to his insane power level but instead resists all their attack however his mask breaks and he is seen and recognised by them all which causes them to halt and he "flees". To make this even more interesting lets say his sadistic n forceful elder sister develops a brother complex for him eventually even though she wants to reject it in her mind, eventually the story progresses and he defends the demonic capital but cannot completely defend all sides of the empire so in an agreement to not destroy the demonic empire he is taken hostage by the heroines for some time where he tries to emotionlessly not speak and doesnt dare look at the heroines faces but is threatened by them that they'll destroy the demonic empire if he doesnt obey their commands and they commands they have relate to their weird fetishes (you decide) whilst his elder sister who has realised by now that she has a complex tries to take this chance to take his purity. He manages to run however is forced back through threats, he then is taken through all the countries as a hostage and meets each goddess seperately etc and so on you continue the story how you like

if you read this thank you for considering my idea, my imagination is a bit wild yes and let me know if you've taken my idea becauss i would love to read it

 

I've had this idea for a while now, but basically MC got transported in a world where every famous literature monsters exist such as Lovecraft's Cthulhu and stuff. My knowledge on such monsters and books are pretty shallow, so I'll leave this idea here.