Bleach: How Powerful Is Ulquiorra’s Cero Oscuro? and Las Noches size

Bleach (anime) episode 271

Cero Oscuro is one of the most powerful techniques used by the Espada Ulquiorra, alongside Lanza del Relámpago. But how powerful is this attack really? We know, based on Ulquiorra’s own statements, that it is capable of destroying Las Noches, and we also saw that it caused massive destruction to its roof. Because of this, we will attempt to estimate its destructive output and determine what level it would reach when compared to natural disasters.

Size of Las Noches

Determining the size of Las Noches is problematic due to the lack of official data regarding its dimensions. Statements made by Nel about the distances between the gates do not align well with the visual representations shown in the manga. This has led to ongoing debate within the fan community about its true size, with estimates ranging from a few dozen kilometers to sizes larger than the state of Texas. This inconsistency is not unique to Las Noches and appears repeatedly throughout the manga; another clear example is the Seireitei in Soul Society.

The only detail we can state with certainty is that Las Noches has a cubic structure and features a dome on its surface.

Therefore, I will attempt to establish a reasonable size based on all the available information.

Bleach chapter 248

Based on Nel’s statement, the gate of Las Noches was three days away from their current location, clearly assuming travel on foot. However, the statement does not specify their exact position, so from this point onward we must make several assumptions.

They were located at the opposite extreme of Las Noches, meaning they needed to cover half the perimeter in three days, and a full loop would take six days.

The three-day journey assumes 24-hour days, from which we subtract 8 hours of rest per day, resulting in 16 hours of walking per day.

An average walking speed of 5 km/h is assumed.

Under these conditions, the total distance covered in a full six-day loop would be:

D = 5 km/h × 16 h × 6 = 480 km (480,000 meters)

Given that Las Noches has a cubic shape, each side would measure 120 km (120,000 meters), resulting in a surface area of 14,400 km².

For comparison, the total area of the Tokyo metropolitan region is approximately 13,500 km², meaning Las Noches would be larger. Another way to visualize this scale is by considering the straight-line distance between Tokyo Bay and Mount Fuji, which is about 100 km. A single side of Las Noches would exceed that distance..

An approximation of what the nights would look like over Tokyo

Cero oscuro.

With a reference scale already established, we can now compare and estimate the destructive yield of Ulquiorra’s Cero oscuro, using the visual perspective shown in Chapter 347, where the aftermath of the attack is clearly visible.

Bleach chapter 347

Side length: 120 km = 1010 px

Height (up to the central dome): 240 px = 28 km

Explosion diameter: 450 px = 53 km, resulting in a destroyed area of 2,206 km²

The remaining unknown is the depth. In this case, we know that the dome functions as the roof of Las Noches.

Bleach chapter 351

Height: 24 km = 370 px

Roof thickness: 8 px = 0.52 km (520 meters)

Yield Estimation

To determine the yield, two approaches will be considered: one based on destroyed area, and the other on volume of vaporized material.

1) Destroyed Area

For this method, we apply the Glasstone & Dolan / Kingery–Bulmash airblast model, using the following relation:

$Y = \left(\frac{x}{0.28}\right)^3$

Where:

Y = explosive yield in kilotons of TNT

x = blast radius in kilometers

0.28 = empirical constant corresponding to 20 psi overpressure

Substituting our values:

$(36.5 / 0.28)^3 = 2,215,156 \text{ kilotons of TNT}$

This corresponds to 2,215 megatons of TNT, an extremely large explosion.

2) Vaporization Method

The destroyed area is 2,206 km², and the roof thickness is 520 meters, giving a total vaporized volume of:

$1.14 \times 10^{12} \text{ m}^3$

As seen in both the manga and anime, the roof appears to be solid rock. Assuming a density of 2,500 kg/m³, this results in:

$2.86 \times 10^{15} \text{ kg of vaporized rock}$

Based on Table #1, vaporizing 1 cm³ of granite (2,500 kg/m³) requires 26 kJ/cm³. Since 1 kg of granite occupies 400 cm³, the energy required per kilogram is:

$400 \times 26,000 = 10,400,000 \text{ joules}$

Due to density variations, a rounded value of 10 MJ/kg will be used, consistent with the approach taken in the Warhammer 40K Exterminatus analysis.

Total energy:

$2.86 \times 10^{15} \times 10,000,000 = 2.86 \times 10^{21} \text{ joules}$

This corresponds to 683,556 megatons of TNT, or approximately 683 gigatons, comparable to the estimated energy released by the Santorini supervolcano (~1 × 10²⁰ joules, or 23,900 megatons of TNT).

Adjusted Vaporization Estimate

According to explosion physics, only a fraction of the material would realistically be vaporized. Following the methodology applied to the Gamera explosion, and using the Sedan nuclear crater yield of approximately 39,554 J/kg, we obtain:

$3.825 \times 10^{15} \times 39,554 = 1.51 \times 10^{20} \text{ joules}$

This equals 27,007 megatons of TNT—still an enormous figure, but much closer to the area-based result. Considering later feats and scaling ranges, this value should be interpreted as a maximum plausible yield, rather than the higher gigaton estimates, though this ultimately remains open to interpretation.

Final Considerations

The wide range—from tens of thousands to millions of megatons—arises primarily from uncertainty in the estimated size of Las Noches. If its side length were 10 times smaller (12 km instead of 120 km), the surface area would be 100 times smaller, and the volume nearly 1,000 times smaller.

However, assuming the size estimate is reasonable, the resulting yield is also reasonable. This places Ulquiorra at a level comparable to a massive magnitude 9.5+ earthquake or the energy output of a supervolcanic eruption.

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