A Record of a Mortal's Journey to Immortality: Immortal Realm - Chapter 1347: Repetition

After breaking up with his girlfriend, he accidentally acquired a genius system and rose from there against the heavens, becoming invincible..

- Description from Novelupdates

Stealing Heroine from Protagonist with SystemWARNING MATURE CONTENT!!!!!R-18

“Kat, you have a tail” said Lily

“Look, Lily, it really isn’t that big of a concern” said Kat

“You.Have.A.TAIL KAT” said Lily “How is this not a concern to you?”

“Well, the dream I had was a bit weird as well, but if I’m honest, I’m mainly worried about the floating text that’s on fire” said Kat

“THE What?” said Lily

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Join Kat on her dimension hopping adventures as she fullfills her demonic duty and answers the call of the summoner. Each week Kat will get involved with new strange situations and oppurtunites that await her. During the week she'll have her best friend Lily, and perhaps a little help from Sylvie to figure out what's she supposed to do with her life now that she's becoming a demon.

Amamiya Hiroto is unlucky. His life consisted of misfortune after misfortune, culminating in an unlucky death during an incident on a school boat trip, trying to save a girl he barely knew. After death, he met a god of reincarnation who requested that the hundred or so dead passengers—one of them being the girl he tried in vain to save—be reincarnated into another world.