We know Stoutland is old, perhaps dying. Maybe, by this point, things have gotten worse for it, and Litten is stressed about it. But we'll get to that later.
I think SM16 will be a more eventful episode than people expect for Litten. In that episode thread, a lot of people are expecting Rowlet and Popplio to talk about their experiences with Ash and Lana resrespectivelRowlet could talk about
Ash's backpack the events of SM04, how much it enjoys battling with Ash, and whatever else it wants to talk about. Popplio can talk about how Lana rescued it from Team Skull and how much it likes fishing with her, maybe even the bubble dream. Both of these stories help Litten to begin to realize that not all humans are bad. Maybe not change its mind, maybewe'll learn about Litten's backstory, but it's enough to get it thinking.
But Litten won't learn that Ash is Rowlet's trainer until the end of the episode. Rowlet is certainly airheaded enough to not mention that.
Anyway, Litten will be surprised that the trainer Rowlet is so fond of is Ash is the same goofy kid from earlier. Ash and Litten will interact briefly (probably nothing more than Ash recognizing and thanking Litten) and Litten will run off. Remembering the events of SM07 and Rowlet and Popplio's experiences with their trainers, Litten takes an interest in Ash and starts following him. Not be use it likes him, but more because it's curious about him.
SM17 and 18 won't have any events of consequence, but there will be shots of it watching Ash and witnessing more positive interactions between Trainer and Pokemon.
Now SM19 will be interesting because this is where I think Litten will witness two Z-Moves used by Ash. Watching Rockruff use Breakneck Blitz to defeat the Mudbray will catch Litten's attention, but Ash's battle with Tapu Koko is going to be what
really sells Ash on Litten. I still expect Ash to lose that battle, but I think Pikachu will put up a better fight and show off a more powerful Gigavolt Havoc. I also think that losing to Tapu Koko is what's going to convince Ash that he needs more Z-Crystals.
BUT before Ash begins the Akala Island trials, I do think SM20 is going to be Litten's capture episode. I don't know what's going to happen or if it's going to involve Stoutland's death (considering Litten's nightmare back in SM07, I think it might). If it does, then maybe Litten will decide to go along with Ash because it has no one else to turn to. Maybe it blames itself for Stoutland's death and wants to get stronger. Maybe Ash and Litten are successful in saving Stoutland, and Stoutland convinces Litten to go along with Ash like Toucannon did to Rowlet. Either way, I think that is when Litten will join Ash.
But I still don't think it will share a strong bond with him. I think it will see him as more of a means to an end without the knowledge that Z-Moves require a strong bond between Trainer and Pokemon.