A/N: Requested by UrielGonzalez574503, and the crossover involves RWBY, Highschool DXD, Trails of Cold Steel, Fire Emblem Engage and Rune Factory.
(Y/N L/N was an ordinary teenage boy who used to have a girlfriend, but everything changed when he caught her cheating on him with his bully Shade. Feeling heartbroken, he starts running, not knowing where he was going, but next day, his life changed for the best.)
(Y/N is seen currently in a school's infirmary as he sees a blonde girl sleeping next to him.)
Y/N: Is that...
(Suddenly she wakes up and hugs him, giving him a passionate kiss.)
Asia: Feeling better, my love?
Y/N: Uh... I don't think I know you...
????: We can understand your confusion, Mr. L/N.
(He turns to see Ozpin, Sirzechs and Vandyck along with several staff members.)
Y/N: And who are you?
Ozpin: My name is Ozpin, and these are Sirzechs Lucifer and Vandyck.
Sirzechs: We are the headmasters of a prestigious hero school we proudly call Union Academy.
Vandyck: We would like to have you as a student here.
(The students who overheard the conversation had different reactions. Some had doubts, others were happy, and there were a few who thought the headmasters were kidding.)
Ruby: (excited) A NEW STUDENT? THIS IS THE BEST!
Weiss: Hmm... I'm not so sure about it...
Cardin: They're bluffing, aren't they?
Weiss: What if they're not? Are you jealous?
(Cardin gets angry and is about to hit Weiss, only to get a slap on his wrist as he turns to Glynda.)
Glynda: (stern) WHO HAD THE IDEA OF SPYING US WHILE WE WERE HAVING A TALK WITH OUR NEW STUDENT?
(Everyone points to Teams CRDL and SSSN.)
Glynda: In my room. NOW!
(The eight growl in annoyance as the girls giggle.)
Blake: Serves them right.
Jaune: Good thing I have a girlfriend.
Issei/Kiba: (in unison) Same.
(Back to Y/N and the headmasters, they notice some kind of power he has.)
Ozpin: Y/N, I feel an immense power within you. You will fit here in no time.
Sirzechs: I'm sorry about Asia though. Not even my sister would have seen her this... you know...
????: But I must admit he makes a good husband material.
(Everyone turns to see Rias herself.)
Sirzechs: How long have you overheard our conversation, sister?
Rias: Long enough.
(Rias then approaches Y/N and hugs him while Asia does the same thing.)
Vandyck: This will be a long day...
(Timeskip)
(Y/N is seen preparing to fight Teams CRDL and SSSN.)
Cardin: I hope you're ready to lose.
Y/N: Funny of you to say that...
Cardin: (stern) You will regret these words!
(Then the eight charge at Y/N, who then launches a chained spear from his own hand as it stabs Cardin's chest. He then pulls him close to him.)
Y/N: GET OVER HERE!
(He then uppercuts him before summoning a shadow of himself as it slams Cardin down. Russel tries his luck, but then Y/N spits some acid which hits his face.)
Russel: AAAAAAAH! MY FACE!
(Dove and Sky angrily charge at him, but suddenly he forms a smoke screen as both of them cough.)
Dove: (coughs) Who is he anyway?
Sky: (coughs) We need to get him...
(Y/N then appears in front of Neptune and freezes him before slamming Sun with telekinesis. Sage charges at Y/N, only for him to punch him with a glove made of sand. Finally, he summons some thunder which hit Scarlet. Their auras dropped significantly as Glynda announces.)
Glynda: And the winner is Y/N L/N. (in mind) Just as to be expected.
Alear: Wow, he is really amazing.
Mist: I want to marry him now.
Alisa: We will protect him from anyone who dares to harm him.
Akeno: Ara ara... I can't wait to punish those foolish enough to try it.
Yang: And we'll bring them down with a YANG!
(Everyone groans at Yang's pun.)
Koneko: You're lucky we share the same love for Y/N.
Fie: Let's just kill those bastards and some goldddiggers.
Yunaka: Hiya papaya.
(The girls got really fond of Y/N, and protected him from anyone who dared to insult him as they killed both bullies and golddiggers. Y/N was feeling completely happy until his ex-girlfriend came into picture.)
Y/N: (crosses arms) Oh, hello again... Bitch!
Iris: Look, I know what I did was wrong, but you need to understand I was sexually frustrated.
Y/N: And you chose to let your lust get the best of you, huh? Guess what? I already have new girlfriends. (smirks) And they're right behind you.
Chloe: So you're the one who broke our Y/N's heart, huh?
Arianrhod: Of course she is, the one she was having a relationship with told us before we killed him.
Tabatha: Time for you to die!
(The girls brutalized her to death, and Y/N didn't care at all. After they're done, they hug him.)
Rias: Done, my love. That bitch will no longer be a burden to our love.
Girls: (in unison) We love you, Y/N.
Y/N: I love you too, girls.
(Y/N had lived happily ever after, and Rias became the alpha of his harem after they married once he defeated Riser Phenex.)