Toaru Majutsu no Index SS: Kanzaki - Chapter 5: Marine Prison. NAGLFAR.

After nine years of traveling with her parents, Long Shiyan’s family encountered a group of bandits. Although her parents died, Long Shiyan was able to escape from them with the help of a system. From it, she learned that she was stuck inside the world of a harem novel! In order to revive her parents, Long Shiyan must prevent the protagonist of the original novel, Long Aotian, from capturing wives and attaining a harem. Otherwise, the world would end!

But, after saving a future harem member from Long Aotian’s clutches, why did this girl obtain a more terrifying characteristic than blackening into a villainess…

- Description from Novelupdates

“Look, I don’t need to be the strongest — I just need to be slightly stronger than the guy trying to kill me.”---Zayn Eldrake was nothing more than a nameless extra in the grand tale of summoned heroes — a disposable swordsman in the legendary Hero of Light’s party, fated to die in an early battle against the monsters of the Apocalypse.But when he awakens in this doomed body with memories of his past life, he refuses to meet the same pathetic end.He knows the story. He knows the heroes. He knows their strengths, their weaknesses… and most importantly, their women.With the power of [Devourer’s Pact], Zayn can consume the abilities of those he defeats, transforming himself into something far greater than a mere extra.Strength, magic, divine blessings — everything in this world is his for the taking. And if fate itself stands in his way? He’ll devour that too.

The more ruthless the Palace is, the more miserable the loser will end up—this he understands. But what he does not understand is, why the brother whom he lived together with peacefully in the past, would so heartlessly humiliate him today. Asking him to beg for mercy, asking him to succumb to his knees, and even… asking him to tactfully entertain him. “Yong Shan, ah, Yong Shan, as of today you are the one who qualifies to succeed as a Crown Prince, what exactly is it that you want?”

For the past 16 years, Yong Qi’s gaze was never set on him. Despite being twins with his younger brother, Yong Lin, Yong Qi has always been directing his smile and laughter towards Yong Lin, and to him, Yong Qi deliberately alienates him. He does not understand, they have the same features and looks, and he obviously is his brother too, but why won’t he be intimate with him… as if he is humiliating him. “Yong Qi, ah, Yong Qi, why won’t you understand, what I want is very simple…”

- Description from Novelupdates