Shinka no Mi (light novel)

Shinka no Mi: Shiranai Uchi ni Kachigumi Jinsei (進化の実 ～知らないうちに勝ち組人生～, "The Fruit of Evolution: Before I Knew It, My Life Had It Made") is a Japanese fantasy light novel series written by Miku and illustrated by U35. It began serialization online in January 2014 on the user-generated novel publishing website Shōsetsuka ni Narō. It was later acquired by Futabasha, who have published eleven volumes since September 2014 under their Monster Bunko imprint.

Synopsis
The elf girl, Aria is an adventurer. Her enchanting, lovely features attracts everyone. Her twin peaks are ripened to the point of exploding. Then, being embraced in between those twin peaks was a little animal… his name is Tama.

He looks like to be a cat at first glance, but Aria and her surrounding companions failed to take notice of single detail. Tama, he’s a human who’d reincarnated, given a second chance at life. His true form, it’s not that of an ordinary cat. Instead, he’s a monster of the strongest class, an extremely young behemoth.