Shokushu Makai no Ryoshuu ~Shippo Zeme to Kougyaku ni Kuppuku Shita Juujin Touzoku Yuni

Long ago, the Kingdom of Lanrod was designated as the sealbearer
for the remains of the evil goddess Elixia, so that she may not be resurrected.
The malevolent one called Zodiac sought the final seal to resurrect her, but it was protected by five heroes in scattered fragments.
But after many months, the heroes now returned to Lanrod castle to reunite the fragments.
It was the perfect chance...

Enter Yuni, a thief girl with heightened senses. She felt Zodiac's evil and rushed to inform queen Ixia.

The seal's power was already beginning to fail.
Yuni felt a bitterness that could never be forgotten.
Just then, the tinge of evil again graced her senses.
"Mwahaha, I've got you at last."
"Ack! Zodiac!"
Yuni couldn't disguise her sudden terror, but she mustered every bit of courage she had.
"Take this!"
She lunged with animal swiftness, a throwing knife flung between his eyes as she unsheathed a secret dagger to eviscerate him below.
"Die!"
The knife froze in the air as though it has struck him, millimeters from his face.
His magic barrier had stopped it. No matter, that was enough - the knife had obscured his view long enough to stab him.
But as the low dagger was plunged into his side, in the floor below her magicked into an oilslick. She slipped, for just a brief second.
Enough to miss.
In the moment she took to regain her balance, the ground swelled in a horrific burst of roiling hot flesh as a tentacle spirit was summoned upon her.
"No! Oh god it feels so weird!"
"Mwahahaha. Ixia's cute little pet. I'll turn you into something pretty my own way..."

[From DLSite English]