When you watched "Tengen Toppa Gurren Lagann" years ago, you will remember a man who shares the spotlight together with the main character. Kamina was Simon's "Aniki," while Simon was Kamina's "Blood Brother." Though the anime was finished a couple of years ago (and the plot doesn't have loopholes for season 2), some viewers including myself still don't accept Kamina's death.
Kamina's death is UNnecessary
Most of the viewers say that Kamina's death is necessary for Simon to find his greatness and to grow up as a character. I used to have the same mindset too, because, after that, Simon became the person the Dai-Gurren Brigade looks up.
When there's a problem, Simon will always come up with something and save the day.
Simon's character grew from being a boy who is scared of everything to a man who isn't going to run away from any trouble. His potential was realized, and his spiral power was unleashed, thanks to his Aniki's death.
But if you think about it, Kamina's death is unnecessary. All of Simon's greatest character improvement started when Simon fought side by side with his brother. He began to use his potential whenever he and his Aniki are in trouble. The road might be longer, but Simon could reach his character in the last episode even with Kamina around. Eventually, Simon will be able to believe in himself, and Kamina is there to watch him take the world.
Simon's growth with Kamina
Simon was never an attention catcher, and Kamina is a naturally charismatic person. But it is absurd to say that Kamina's presence will hinder Simon's growth. The thing is, while Simon is growing, Kamina is also growing at a rapid speed. He is similar to Goku when it comes to battle ingenuity. With Kamina's natural charisma, he was able to inspire more people (and viewers) than Simon.
I think Kamina's death is not necessary, but it must be done to emphasize that Simon is the main character. It is sad because Kamina's death feels rushed and too soon.
Nia's special participation
It is not Kamina's death which made the most growth in Simon's character. In fact, when you look at it, Kamina's death made Simon a hopeless case.
It was Nia's character that made Simon grow and be the best spiral warrior in the Universe. He also fought till the end because of Nia's abduction. Kamina's legacy affected the spirit of the Dai-Gurren Brigade and helped them fight against the anti-spirals. But I think it would be a better fight when Gurren's origin pilot is around, telling Simon to grit his teeth in the time of hopelessness.
