One thing I kind of like about the Sun Arcana Social Links or Confidants and the characters associated with them is that they in a way reflect the ending of the Fool's Journey of the respective protagonists involved. The Sun Arcana is close to the end of the Tarot, just before Judgement and World, which are the endpoint of The Fool's Journey, and the themes of the Sun Arcana are clarity, happiness, and accomplishment after the darkness of the Moon Arcana, and in the end being truly fulfilled and satisfied at the end of a Fool's Journey. Akinari, Yumi/Ayane, and Tora's resolutions mirror the respective protagonists' endings at the end of their Fool's Journeys, ie the endings of the games in a way.
Akinari is a rather interesting (if bittersweet) spin on the Sun Arcana's themes, but he fits because even though his whole thing is that he was doomed to die young because of his terminal illness, in the end, he accepts his death not out of resignation, but because he's fulfilled. He writes a book and manages to finish it and give it to Makoto before he dies, and later it turns out his dying words to his mother were of gratitude. He didn't lament how short his life was. He was grateful to her for giving him the life he did have, no matter how short it was, and he's glad to have been born, to have been her son. He did find happiness in the end because he found his answer to life's greatest question, and in his dying moments, he had no regrets. He made the most of his finite life and managed to make it matter through the smallest things, namely the book he wrote and how he will live on through it. Much like how Makoto himself ends up dying in the end because he sacrificed his life to seal Nyx away, but he died fulfilled because he found meaning through the connections he forged, and he also had no regrets. They both died, but they know they'll live on in the ways that matter through the lives they will impact. Akinari through his book, and Makoto through the bonds he made with others and how he impacted their lives, and the lives of those who will be impacted by his friends' lives.
Yumi and Ayane are kind of opposite spins on a similar path of self-honesty. At the start, Yumi pursues acting aggressively and competitively to run away from herself, at the expense of others. At the same time, Ayane is a people pleaser who doesn't think too highly of her talent and sidelines herself and her own dreams and happiness for others' happiness and success. Yumi ends up confronting her own messy feelings about her dad's presence (or lack thereof) in her life but accepts that her parents, even her dad, gave her life, and she gave meaning to theirs, and resolves to live for herself. Ayane meanwhile learns to live for herself and pursue her own ambitions honestly, and despite one quitting drama and the other continuing her path in music they both seek to find ways to contribute to others' lives and bring happiness to others. Both of those mirror the way Yu's time in Inaba ends, because he came at first with no real purpose but left with a sense of clarity of who he is, who he wants to be, and as someone who is able to connect with others and bring meaning to others' lives.
And Toranosuke is pretty different but similar to Ren, since he started out as someone who was framed for false charges against him like Ren was and endured societal disgrace, but managed to win over people as a politician through honesty and sincere conviction in his speeches. He's a politician who is genuinely committed to the values he speaks about and truly believes in them and reforming society, much like how Ren despite being a Persona User and Phantom Thief ends up firmly standing by his values and maintains his principles. They both become the kind of person who inspires change through fighting honestly in what they believe is right, even if they have to endure disgrace in doing so, in their respective paths.
I'm probably reaching and looking into it too much, but it's a nice parallel in all cases. The Sun Arcana characters and their arcs are, in a way, a mirror and microcosm of the answer the respective protagonists themselves reach at the end of their Fool's Journeys, and also reflect who they themselves become in the end.