During the Season 1 finale of The Mandalorian, the beskar-clad bounty hunter's real name was revealed by Moff Gideon to be Din Djarin, and he was a foundling adopted into the creed of the Mandalorian people as a child. Mandalorians have a cultural practice of adopting foundlings, and they don't have a prejudice against adoption versus blood connections.
Also at the end of Season 1, Din takes on a mission to return Grogu to his own kind, and the Child is practically Din's son throughout their journey. In essence, that makes Grogu a foundling; therefore, he could also adopt the moniker of a Mandalorian, which would mean he is the real titular character of the series, not just Din.
At the end of Season 2, Grogu leaves Din to continue his Jedi training with Luke Skywalker, thus completing Din's mission to return Grogu to his own kind, but it does nothing to eliminate the familial like bond that's developed between the characters. Din was part of a specific Mandalorian clan called "The Tribe," which has a creed that is not shared by other clans. This includes an oath not to remove their helmets, and they have a commitment to protecting and fostering foundlings. This is seen when the Armor tasks Din with returning Grogu, saying Din, "will be as [Grogu's] father."
By being a foundling, Grogu becomes a Mandalorian, and this complicates the assumption that Din is the solo titular character of the series. This could lead to several different paths the show may take now that Din's mission with Grogu seems to be wrapped up.
The show could continue to follow Din as he is now the owner of the Darksaber, which makes him the true leader of the planet Mandalore. However, The Mandalorian could shift and follow Grogu as he trains with Luke. The show could also follow both their journeys simultaneously.
If The Mandalorian does the latter, it may lead to Grogu outliving Din depending on how much time passes. Grogu is the same species as Yoda, who was 900-years-old when he died, so if Din died of old age, Grogu would outlive him, becoming the sole Mandalorian in regards to the show.
Grogu choosing the path of a Mandalorian may explain why there is no mention of Grogu during the sequel trilogy of the Star Wars films. He may have chosen the way of the Mandalorian instead of the way of the Jedi. He would not be the first to quit the Jedi order in favor of a different path, as Ahsoka previously did. In fact, the two have already met; therefore, Grogu has already seen others choosing a different path than the Jedi. He could do something similar, embracing the Mandalorian title instead.
Grogu abandoning the Jedi and outliving Din could make him the titular character of The Mandalorian. While the assumption has been -- up until this point -- that the series title refers to Din specifically, developments over the first two seasons may imply that Grogu may surpass Din and become the singular Mandalorian in the end.
Created by Jon Favreau, The Mandalorian stars Pedro Pascal, Gina Carano, Carl Weathers and Giancarlo Esposito. Seasons 1 and 2 are now streaming on Disney+.