Lato women are after foreign billionaires

In chapter 6 - "Identity confusion violation", Toujirou flies to LATO and meets with the cheery man at a resort and he says this:

"All LATO girls dream of falling in love with foreign billionaires", 

But that makes no sense because this is in LATO, LATO is the wealthiest of all the factions of the A3W world thanks to rare spiritium, and the population of billionaires would be much higher than anywhere else. The people there are also much more well off and prosperous than in other factions. 

Women wanting to marry rich tourists is something much more characteristic of very poor countries.
The emphasis is on 'foreign', not marrying just a billionaire but a foreign one.

The consideration is not simply money but marrying a citizen of a different faction other than LATO.    -> Genetic diversity.

Rare Spiritium

First before coming back to the main point we have to untangle the mystery of why only Latin America posseses Rare Spiritium fields. Spiritium is found all across the globe as a natural resource but rare spiritium is found only in Latin America, why is that? Why would a natural resource be in only one part of the globe? That's because it's not true, though only LATO has the technology necessary to harvest it. 

I won't get into what exactly Spiritium is here as it requires it's own insanely long post but the short version of it is that it is a kind of metaphysical petroleum derived from mummified human corpses of the victims of World War III.

There is no 'Rare Spiritium', there is only Spiritium but the difference is that Rare Spiritium is simply  refined in a different way from regular Spiritium. Think of Oil distilliation as an example

< 20°C (Top Tower): Petroleum gases (propane, butane) used for LPG.

20°C – 150°C: Naphtha and Gasoline. Used for gasoline/petrol and petrochemical feedstock.

100°C – 175°C: Paraffin/Kerosene. Used for heating, burning, and solvents.

250°C – 350°C: Diesel/Gas oil. Used for diesel fuel, heating oil, and industrial fuel.

> 350°C (Bottom/Residue): Lubricating oils, fuel oil, and bitumen/asphalt. 

The oil is distilled into different substances. Rare Spiritium is a different way of processing Spiritium.

From the text we know that:

• Spiritium is not energy in itself, it must be converted into energy with a dreiisig conversion
• Only Human brains can perform the dreiisig conversion, computers and machines cannot.

--Spiritium is refined using The human brain and spinal column. 

Regular spinal cords can distill regular spiritium but rare or 'anomalous' spinal cords can distill 'rare' spiritium, - Anomalous spinal cord specimen LD = Lambda Delta.

LambdaDelta

A regular spinal cord has 33 vertebrae in it:

7 Cervical (C1-C7)

12 Thoracic (T1-T12)

5 Lumbar (L1-L5)

5 Sacral

4 in the coccyx

Making up 33 Vertebrae, but sometimes an extra Lumbar bone L6 is present making for an anomalous spinal cord with 34 vertebrae. 33 - Lambda Gamma, 34 - Lambda Delta.

Anomalous spinal cord specimen LD3105

Spines with a sixth lumbar vertebrae can convert rare Spiritium.

In parts of Peru burial sites were found where a very large percent of the buried exhibited an extra lumbar bone. An extra L6 is found in roughly from 1.5% to 7% of people but in this burial site the percentage was around 20%, meaning 1 in 5 people had this trait. It was found that this trait was common in this community because of inbreeding. 

Extra vertebrae and spinal anomalies are frequently linked to inbreeding (although not the only cause) due to the expression of recessive genes that control skeletal development (Hox genes).

The subject of inbreeding is not a new thing in wtc, if you recall in Umineko Sayo Yasuda was born of Incest between Kinzo and her mother who was also his daughter. Sayo's name also means 34 in japanese.

possibly, those people can reach Hinamizawa Syndrome L6.

What's also suspicious is that there is no mention in the story of how LATO regained it's population after WW3, contrary to all the other factions:

AOU, ABN, ACR - Factory birth

COU - Ciconia - natural birth

It's likely that LATO in the beginning of A3W regained it's population with inbreeding due to genetic isolation caused by pretty much everyone else dying with factory birth being rejected.

It's also possible that the as a result of this the culture of LATO favors breeding with outsiders to diversify genes.