I'm starting to feel the presence of the kwamis during the end cards is symbolic of Marinette's new role as the guardian.
If you think about it, any episode where Marinette's new role played an important part of the plot included the kwamis at the end card.
Truth featured the kwamis not only as an explanation to Marinette's new responsibilities and how her Miracle Box works, but also because said responsibilities were a key factor to her breakup with Luka.
The only reason Lukanette broke up is because Marinette couldn't be completely honest with Luka, which resulted in him being akumatised because to him trust and honesty are everything. Luka wasn't even upset at the idea of Marinette not having moved on from Adrien. It wasn't until she told him outright she couldn't be honest with him that his heart finally broke.
Marinette's role as Ladybug, as the guardian of the miraculous, and Shadow Moth's constant meddling are what got in the way of their relationship. The heavy burden Marinette's carrying on her shoulders is getting in the way of her life.
Then we have today's episode: Gang of Secrets.
As you can see above, the kwamis are featured again in the end card. And that is because Marinette's life has become so stressful she's constantly lying and hiding her true self from her loved ones.
The cinema scene hit far too close from home to Marinette's liking. She said it herself: you fall for someone, but you're unable to tell him how you feel. So you wait and try, and try, and try until the opportunity slips through your fingers. And before you know it the boy you love is unapproachable and has a girlfriend himself. Of course, you're heartbroken, but then you fall for a new guy and everything's perfect. In fact, it's too good to be true. Lo and behold, you have secrets you can't tell anybody about, but your boyfriend hates secrets, but since you can't be honest with him, the only choice you have is to break up with him.
That film was a summary of her own love life and, moreover, of what her life was turning into.
Again, she said it herself: superhero movies are better.
Which is exactly the direction Marinette wanted to take her life to!
In the very beginning she was already obsessed with fighting Shadow Moth. Her only concern was stopping his newest akuma. And after talking to Tikki and seeing nobody could really relate to her, she made up her mind. Her double life's too complicated? Fine, she'll choose which life to live from now on. And she chose Ladybug.
It's actually a good thing the girls arrived when they did, otherwise who knows what Marinette could have done.
Luckily, this episode actually ended on a hopeful note. With Marinette finally finding someone she can vent to and be fully honest with.
Then, there's Monster Fu.
Marinette seemed to have a better control over her situation. Chronologically speaking, there are another two episodes before this one showing Marinette's development as the guardian and how she's dealing with it.
Again, this episode revolved around Marinette's new duties. This time she had to convince Su-Han that she is a capable guardian and that Master Fu's decision wasn't misguided, all the while she learned more about her role and the powers that come with it.
As you can see, the kwamis appear once again in the end card.
Do you want to know in which end card they DON'T appear?
Which makes sense once you remember this was an Adrien-centric episode. For once, Marinette was actually a minor character until they had to face off against Lies. Furthermore, the only time the kwamis appear is for a minute or two at the beginning, when they were fooling around Marinette's room.
This episode was all about Adrien and Kagami. And thus, there are no new responsibilities that need to be explored, because Chat Noir doesn't have the same responsibilities as Ladybug. Sure, we saw how packed his schedule truly is, but we all suspected it already because it had been mentioned countless times since Bubbler. In other words, there's nothing new.
While it should be noted that, just like Lukanette, Adrigami broke up due to secrets that couldn't be shared, we have to keep in mind that the difference between the two is that this is actually an exploration of how Adrien's relationships would turn out with him constantly having to take a rain check because of responsibilities he already has. While Truth was about exploring Marinette's relationship with the EXTRA BURDEN of being the guardian.
Summing up, if the kwamis play any sort of significant role, the chances of the episode focusing on Marinette as the guardian of the miraculous are pretty high.
