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Oooohhh! That's a good theory! THAT may be why Endo and Kobayashi can talk to the characters in the otome game! Endo has more difficulty because he's Bard but Kobayashi has an easier time because Finne also has the same power as Sieg, and maybe it kinda works both ways, like you can hear the voices of otome game characters and thus talk to them, kinda like what Sieg and Finne are doing in reverse?
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Alright....since I still didn't want to give some major spoiler since I really love the surprise, I tried to be as precise as possible...
Basically, the only reason Endo and Kobayashi can connect to the otome game world is because their feelings resonates with Liselotte's feelings that love Sieg so much (the main reason they played the game is because Liselotte after all).
The world is real and the otome game is just a bridge between the two world.
In the end, both Endo and Kobayashi will attend Liese and Sieg's wedding.
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And here you go...this is some illustration from the novel. Just scroll to the last pic
https://mwmtranslations.com/2019/08/09/endo-and-kobayashis-live-commentary-on-the-villainess-v2-illustrations/
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I just briefly explained what the pictures about...starting from picture 5:
Pic 5: Sieg is madly jealous when Liselotte is being chummy with a genius student of the academy, which is younger than them, which is one of the capture target of the otome game.
Pic 6: Finne beat up both Liselotte's father and Baldur. They're on the verge on getting into a fight (as in the duel between two knights) because Liselotte's father didn't want Finne to marry Baldur and Baldur wanted to marry Finne (there's no marriage talk tho. The topic arose just because Finne is holding Baldur's hand and Liselotte's father going into a stupid father mode while Baldur is already stupid)
Pic 7: Liselotte woke up from her ordinary nightmare. But this time she's fighting back. And she had made a resolution that she will marry Sieg even though her love is unrequited (Rize-tan you silly girl...you....you)
Pic 8: Kobayashi is overjoyed when Liselotte and Sieg finally confessed their feelings to each other
Pic 9: I'm not sure about this one. Maybe Baldur is being embarrassing again
Pic 10: Sieg and Liselotte dancing during the autumn ball. They're wearing knight uniform in preparation to fight the ancient witch
Pic 11: Together, they're waiting for the ancient witch to appear
Pic 12: Final showdown aka verbal assault with Kuon Kirise
Pic 13: Endo and Kobayashi is saying their goodbye to Sieg and Finne
Pic 14: Both Endo and Kobayashi was isekai-ed to the game world to congrats Sieg and Liese on their wedding. They don't know what to wear, so, they just wear their school uniform <( ̄︶ ̄)>
Okay okay hear me out.. BUT FINNE AND KOBAYASHI HAVE TO BE … in some way … THE SAME PERSON AND THE SAME GOES FOR ENDO AND BARD (sorry if I spelt it wrong but the guy who finne is dating now) TELL ME IM WRONG