outline

In a village lies the village coward, a young man who is easily scared by anything.  People love to scare him, and don't really take him seriously.  All villages picks out a hero each year (identified by a light from the heavens), who goes out to find and kill the Succubuss Queen, all of which fail and become Incubi themselves, or have a fate even worse than that.
Village Coward has obvious childhood tsundere friend.  She likes him, he thinks she hates him.  She plays the most pranks/scares on him.

One night, an invasion is held by the Succubus Queen, and the hero chosen this year has already fallen.  So people panic.  Women are jailed and men are forced to have sex on the spot whenever they are caught.  Village Coward stealthily avoids a lot of the Succubi, but before he could get to the edge, is discovered and brought to the Queen.  Queen then comments on him being honored to have sex with her, and as she reaches for his head, he screams and passes out.

He wakes up, feeling normal and fully clothed, but with sore arms and hands.  When he looks at himself though, he's covered in blood, and he's sitting on a bloodily beaten body of the Succubus Queen.  She weakly begs him to kill her, but he backs away and onto the floor, scared at the sight that beholds him.  As he looks around, he sees the other Succubi looking at him with fear in their eyes, then proceed to make a hasty retreat, taking the Queen, who is begging anyone to kill her and put her out of misery.  As they fled, a familiar light shines onto the coward...

Coward refuses the call, but is forced out the village to pursue the Queen.  However, Coward is not questing to finish off queen; rather, he goes on a quest to find another hero to do that. With only his pet mantis at his side, he goes off into the world of Monster Girls.

However, a few steps outside and he discovers a Succubus, who admires his carnage of the night and wants him to beat her like that.  As such, he is now being followed by a masochistic Succubus, who tries to tempt him into slapping/spanking/pummeling her for gratification.

Tsundere girl follows him sometime later, worried that the succubus will do things to him.

Characters:

Village Coward is a coward; scared of almost everything, especially succubus and monsters.  Somehow bloodily beats up the Succubus Queen, and is on a quest to find a hero to finish the job.
The only thing he isn't scared of, for some reason, is bugs.  As such, when the mantis he carried along his journey turned into a monster girl, he doesn't scream in fear of it; rather, he treats her like his best friend, much to the dismay of Tsundere girl.  Also doesn't overly panic towards other bug-like monster girls.
Turns out that Village Coward is able to manifest his fear into his fist to smash into someone.  The more fear he develops, the stronger the power.  Essentially, he beats his fear into someone else, identified by a shrieking sound (http://www.youtube.com/watch?v=RAcXAmLCtdg&feature=share&list=FL9CJVowyN_i861rCehjcMxg&index=26 skip to 5:20 for referece).
As a coward, he has no qualms about abandoning those that he is afraid of.
Eventually discovers that he inherits this power from his father, an alchemist who has learned to manifest emotion into the physical world.

Masochistic Succubus girl saw how coward beat up the queen, and fapped quite vigorously to it.  She "fell in love with his carnage" and is actively trying to get him to spank her, beat her, and do other kinky/violent stuff.  Protag may or may not do those things to keep her in check in fear of getting raped by her.  Doesn't care about his fear of everything unless it gets in the way of her advances.
Overtime, she develops to be more loyal to coward than to the Succubus Queen.

Mantis girl was created from his pet Mantis.  As the protag isn't afraid of bugs, Succubus thought of something to get past his fear by (somehow having sex) with said mantis.  She too, is loyal to coward, and teaches him further stealth strategies to avoid being detected by other monster girl species.  Falls in love with him.

Tsundere girl is cowards "childhood friend."  She likes him, but is mean to him.  When she discovers that a succubus is following him, she gives chase, in fear that she may take him away.  Attempts to confess to him, but confession falls flat to him, as he is too scared to believe it.  Realizing this, she tries to treat him better, but is too late when he abandons her with a group of feral succubi.
Will likely make a comeback, but not sure if it will be friend or foe.

Fuck somehow this became a tiny harem.  Shieeet.