Okay so, favourite troupe in a shounen manga/anime?
I have one that's my total fav - redeemed villain who's now part of the main group🥰 (example: Piccolo & Vegeta from Dragon Ball) - and besides the cool fights, this is the other reason why I absolutely adore shounen series! ❤️
That is also one of my favorite tropes 🥺 I love when the shounen stipulates that the villain isn't fully redeemed and they're still very capable of doing questionable things, because that really shows that it's not like the villain is magically cured, but there's some level of understanding between the villain and the heroes side.
And I definitely love the trope in which characters with questionable moral (can be villains, ex-villains or former antagonist) start teaching or protecting little kids or younger characters. I adore to see how both the kids and the adults learn from each other, their mutual understanding and respect, the way the characters with questionable moral decide they're only soft with the kids or the way the kids become powerful enough to protect the morally questionable characters.
The pure nature of the kids along with the lack of judgment they provide sometimes help the gray characters find a reason to grow and overcome themselves. Also, the kids can learn from an early age that everything is not black and white, that they don't have to hate everything or love everything, that just because something looks a certain way it doesn't mean the looks match the content.
There are some examples of this is Dragon Ball (Gohan and Piccolo), on Naruto (Zabuza and Haku), on Katekyo Hitman Reborn! (most of the mentors of the Vongola Family) and there are some on Boku No Hero Academia as well (Kurogiri and Tomura, Twice and Toga), etc.
It's a really cool trope because it has my favorite things in the world: complex characters, kids, friendship or platonic love, lack of sexual interactions and found family, among others.