☆Blue girl☆

1. Biological Foundations of Human Fertility

Human fertility is constrained by a very narrow biological window. Although ovulation itself only lasts 12-24 hours, viable conception can occur during a broader timeframe due to sperm survivability.

Key Biological Parameters:

Ovulation window: ~1 day

Sperm viability inside the vagina: up to 5 days

Effective fertile window: Approximately 6 days per cycle.

Pregnancy can only occur during this limited fertile interval. Assuming a standard 28-day cycle, only 6 out of 28 days (≈21.4%) allow for viable conception.

However, in reality, the percentage is actually lower because those 6 days do not have the same probability of resulting in a successful pregnancy.

2. Probabilistic Assessment of Single-Act Conception

From Google, we can assume that the following average probabilities of conception per unprotected intercourse:

During ovulation: 25–35%

1–5 days before ovulation: 10–20%

≥6 days before ovulation: <1%

After ovulation: ~0%

Across the entire cycle, the mean per-act conception probability for intercourse occurring on a random day is:

𝑝≈0.04–0.07

For the following mathematical modelling, I will use the mid-range value of p = 0.05 (5%)

In simpler terms:

Probability of getting pregnant from a single encounter -> p = 0.05 (5%)

Probability of NOT getting pregnant from a single encounter -> 1-p = 0.95 (95%)

This is a very low-probability event.

3. Cumulative Probability for Multiple Sexual Encounters

As you might be aware, pregnancy becomes significantly more likely when intercourse occurs repeatedly across the menstrual cycle.

So... how many encounters would Nero's mom and Vergil have had, to realistically, have created Nero?.

For independent events, the probability of not conceiving across n unprotected acts is: (1−p)^n

Thus, the probability of conceiving at least once across n acts is:

P(Pregnancy) = 1- (1-p)^n

As you might have already noticed, the probability is exponential, not linear. But let me show it to you with the math. n = N° of unprotected sexual intercourse.

n =1:

P=1−(0.95)^1 =0.05 (5%)

n = 3:

P=1−(0.95)^3 =0.143 (14.3%)

n = 5:

P=1−(0.95)^5 =0.227 (22.7%)

n = 10:

P=1−(0.95)^10 = 0.402 (40.2%)

n = 20:

P=1−(0.95)^20 = 0.642 (64.2%) -> Only after the 20th encounter does it start to become an actual possibility for someone to get pregnant.

n = 30:

P=1−(0.95)^30 = 0.785 (78.5%)

After the 30th encounter of unprotected, penetrative sex, it becomes extreamly likely to produce offspring. However, we can take this further...

In probability theory, the expected number of independent Bernoulli trials required for one success is:

E = 1/ p -> Given that p = 0.05, the expected number of randomly timed unprotected encounters required to produce conception is E=20

What does this mean? On average, around 20 unprotected encounters are required for conception when intercourse is not timed for fertility. Which means, Vergil and her must have seen each other at least 20 times. Of course, without mentioning that this only counts for penetrative, penis in vagina sex, not other forms of intercourse -> And also assuming that Vergil has the weakest pull-out game known to mankind

We can also do inverse logic using a Bayes-adjacent reasoning.

A = pregnancy occurred

B₁ = conception from one act

Bₙ = conception from n acts

𝑃(B₁ ∣ 𝐴) ≪ 𝑃(Bₙ ∣ 𝐴)

That is, the posterior probability strongly favours multiple encounters once pregnancy is known to have occurred.

Thus, within the narrative, the existence of Nero is itself statistical evidence that Vergil and his mother were engaged in more than one sexual encounter.

4. Conclusion for my lazy bastards who cannot be bothered to read all that.

Both biological reality and mathematical modelling indicate that:

A single unprotected encounter has a low probability (~5%) of resulting in conception.

Multiple unprotected encounters dramatically raise the likelihood of conception (to 20%, 40%, 60% and beyond).

The expected number of random-cycle encounters needed to achieve pregnancy is approximately 20 or more.

Therefore, it is statistically improbable that Nero was conceived during a one-night event.

Authors Note

This was for the funsies and the funsies only. I'm 100% certain that the developers and writers at Capcom were not applying probability theory to Nero's conception.

I'm sure that Capcom itself doesn't even know who Nero's mother is— they purposely left her identity and relationship with Vergil ambiguous. So, if they choose to reveal it someday, they have the flexibility to say it was either a one-night stand, a situationship, or a fully fleshed-out relationship.

Furthermore, one could argue that Vergil is exceptionally unlucky, hilariously so. I mean, my man hasn't had a day of peace since he was born. Given his narrative tendency toward misfortune, it is conceivable (pun intended) that he could fall into the improbable 5% scenario of impregnating someone in a one-night stand, purely out of the writer's spite, of course.

Nevertheless, the numbers don't lie...