Surprise sex

Surprise sex is one of two options of capturing a Nephelym (the other is giving them their preferred fluid).

Both the Wild Nephelym or the Breeder (if they have at least 600 Lust) can initiate it. Surprise sex can only be initiated if the receiver is either the opposite sex or futanari.

During the sex scene a climax box will appear on the top-right of the screen. This shows how close the Nephelym and the Breeder are to their respective climax. When the Breeder climaxes first it will cost 600 Lust and will not allow the player to catch the Nephelym. However if the Nephelym is to climax first it will refill a portion of the Lust gauge and will allow the player to choose whether to catch it or leave it. You need to click rapidly to resist climax.

If a Nephelym started surprise sex with you, when you had 0 Lust, and you lost it, then you enter the Endless Daze. You will be teleported back to your last activated shrine and the Reaper will take her toll.

Nephelym with different height have different sex animations. Every height has 4 sex animation: submissive male, dominant male, submissive female, dominant female. Wild Nephelym sometimes have surprise sex with each other, the player can't interact with them until they finish.

Spontaneaus Blow Job
Spontaneaus Blow Job is a subpart of the surprise sex system, and it happens randomly. Only the receiver's climax meter is rising. The Breeder can't do anything during the blowjob and the success rate is around 50%. If the blowjob fails, the Breeder loses 600 lust (or all remaining lust if they had between 50 and 550); if they had 0 lust, they instead succumb to the Reaper.

Only female or futanari Breeder can initiate Blow Job upon a Nephelym, and only if that Nephelym is Normal height (6ft) or smaller.

Spontaneous Blow Job has a low chance of happening (perhaps 10% of the time, anecdotally).