or is it something unique only to rou as a living god?

as of right now know. anyone who has or mill reach tier 5 has a blessing. In the web novel, it appears that opushii and her "twin" siblings become overlords but there does not seem to be much in the way of visuals right now. The light novel reached this point so there will likely be images but for now nothing since no one has purchased it. However, it should be noted that these 3 children can be used as refernce to figure out what a base will look like since it doesn't seem that they have extra arms like their father. (see day 452)

I stand corrected, Auro and Argento both have overlord forms in the game. At least thats what their descriptions say. visually, they appear to be the same and the species is still lord mixblood

Edit: granted they are mixbloods

That is what they are now, "Overlord Mixbloods" more or less? Or am I misunderstanding you?

Here are some images. Here can see in the game description (to the right), it says she is an overlord/lady but then the race mentioned in on the same unit's profile page (below) is lord mix blood. There is a strong possibility that the former is a mistake and the latter is correct.

I did not do too much reading of the dc but i remember them going through a forest and training and fighting a boss and then they rank up on day 451 and their abilities and new appearances are shown on day 452. 

Among such children, the first one to evolve was  Ouro and Argento, whose tribe was 【Mix-blooded Lord】 now 【Mix-Blooded Tsukunagiri · New Species】. 

The apparent change is that the body has grown as many as a few years old. (?His body has grown to the size of few years old kid) (Their bodies grown a few years older than before imo)

The Three  Orbs at the center of both hands and chest were added to both shoulders and become five at the end .

The (?Living armor) bodied armor (?was replaced by )  clothes which looked like the mixture of Japanese  and Western style armor.

Then it seems that the number of corners has increased and the  tattoo becomed darker

-Rou on Auro and Argento's rank up (Day 452)

 

These images from the DC (left and right) and the images of the war (below) show that there is no apparant change in there appearance. There for, the mistake is proably in the game description but I show this in order to give all the information. 

Okay, I understand now. Thanks.

They don't seem to change very much with each Rank Up it seems, they look almost the same when they were Ogre Mixbloods.

still this make wonder the differences between their rankups, as well as what the other childrens overlord forms will be

day 452 explains their rank ups if you can understand it. net too well tranlated, especially the species names.