Among all supporting characters besides Doraemon, who has had the greatest impact on Nobita's growth?

Okay, let's talk about this.

This is a very interesting question. While Doraemon is the obvious "cheat code," Nobita's growth is undeniably shaped by everyone around him. Picking just one person with the most influence is difficult because they shape him in different ways.

But if I must give one answer, I'd cast my vote for two people who act like two sides of the same coin, jointly influencing Nobita's development: Gian and Shizuka.

However, there's also a "hidden" best candidate whose influence runs even deeper – we'll get to him last.

1. Shizuka: The "Lighthouse" and "Goal" of Nobita's Growth

Shizuka's influence on Nobita is positive guidance. She's like a lighthouse on Nobita's life path, showing him where the "good direction" lies.

A Benchmark for Morality and Kindness: Shizuka is kind, clean, and compassionate. Often, Nobita's initial motivation to "be better" stems from a desire for Shizuka's approval. For example, he might muster courage to appear brave in front of her, or try to do the right thing because he doesn't want to disappoint her.
The Goal for the Future: We all know Shizuka becomes Nobita's wife. This setup itself means that much of Nobita's lifelong effort revolves around the core goal of "how to become someone worthy of Shizuka." To achieve this, he must overcome his laziness, cowardice, and other flaws.
Emotional Comfort: When Nobita is bullied or wronged, Shizuka is often the one who offers him gentleness and comfort. This warm support is a crucial reason Nobita doesn't completely lose his way amidst setbacks.

Simply put, Shizuka defines the standard of "good" and is the beautiful goal Nobita strives to reach.

2. Gian: The "Whetstone" and "Catalyst" for Nobita's Growth

Gian's influence is the opposite: negative pressure. He's like a rough whetstone; the process is painful, but it genuinely forces Nobita to grow.

Creating Adversity, Sparking Courage: Gian's bullying is the biggest source of "suffering" in Nobita's daily life. It's precisely because of this formidable opponent that Nobita is repeatedly pushed to the brink, forcing him to summon courage and resolve he doesn't usually show. In many movies, when facing real danger, Nobita's ability to step up is inseparable from his experiences standing up to Gian.
Forcing Nobita to Reflect and Seek Help: If life were smooth sailing, Nobita might remain lazy forever. It's Gian's constant trouble-making (stealing comics, forcing him to play baseball, holding concerts) that compels Nobita to think "what to do?" and turn to Doraemon for help. While reliant on gadgets, this cycle of "problem-solving" is itself a form of growth.
Highlighting Nobita's Kindness: Sometimes, even when facing Gian who always bullies him, Nobita will lend a hand when Gian is in trouble. This "returning good for evil" behavior becomes especially valuable precisely when contrasted against Gian's "badness," allowing Nobita's own kind nature to shine through and solidify.

Simply put, Gian is the "villain" constantly throwing challenges Nobita's way. But it's precisely these challenges that give Nobita the opportunity to level up, gain experience, and grow. Without Gian, Nobita's courage and kindness might forever remain theoretical.

The Final Special Nomination: Grandma (Obāchan)

If Shizuka and Gian influence Nobita's "behavior" and "social interactions," then Grandma (Obāchan) influences Nobita's "heart" and "foundation."

Grandma appears very rarely, mostly in Nobita's memories and time-travel visits. But her impact is nuclear-level.

She is the only person in the entire story who gives Nobita 100% unconditional trust and love.

When everyone else thinks Nobita is useless, calls him stupid, or is disappointed in him, only Grandma gently tells him, "You will surely become a wonderful adult someday."
She never demands Nobita get 100% on tests, nor cares if he's better than others; she simply loves her grandson purely.

This unconditional love gives Nobita the deepest, most solid sense of security within. It allows him, after countless failures and self-doubts, to always retain a place of softness and kindness in his heart. He knows that in this world, someone once believed in him so profoundly.

Conclusion

So, my view is:

At the day-to-day and behavioral level: Shizuka and Gian, acting as positive and negative forces respectively, together constitute the main external drivers pushing Nobita's growth.
At the spiritual and emotional level: Grandma's influence is the most profound. She shaped the kind core of Nobita's character and the foundation of his personality; she is the soul who makes Nobita truly "Nobita."

If I absolutely must choose one "most" influential person, I would cast this most special vote for Grandma. Because her love is the starting point for all of Nobita's growth.