Viral appears for the first time in Episode 2, and there Kamina and him have a fight. Stubborn vs Stubborn, Sword vs Sword, many sides of their peronalities are very similar, this is the reason why we can say that a side of Kamina is a beast and a side of Viral is human. XD
I'm kidding LOL, but they're really similar.
Viral introduces himself as the commander of one of the team of the Spiral King, and it's battle at once. Kamina and Simon with their Gurren Lagann and Viral with his Gunman Enki.
Many times Kamina and him share a fight but Viral always turn back, even if he's k.o. and even if he's enjured.
Viral's body is special, because be a Beastman means to have an immortal body, and even if he has scars, he doesn't die.
Viral considers Kamina his rival and he tries to fight against him in each situations. This is the reason why he's part of Commander Adiane's troups and he asks to her to fight instead of her (but obviously she wants to fight alone).
Adiane's death is a difficult moment for him and that is the first time
in which we can see Viral that cries bitter tears.
He's a Beastman but he has strong feelings, many sides of him
are human and even if he hates humanity and its "presunt" intention to overpowered Beastmen, Viral knows that not all of them are evil.
Simply, he prefers to fight together his comrades, creatures like him that are feared to be killed by humans.
Their goal is be free and to live happily like all the creatures of the world, they are not different and surely they are not inferior.
Kamina's death is also a moment of careful consideration for Viral, that decides to makes Simon his new rival.
But in a first moment, Simon, shocked by Kamina's death, isn't able to fight against him as Kamina made, and Viral isn't soddisfated.
When Simon finds again the way to live and to fight, Viral fights against him like he precedently made with Kamina.
But Viral isn't a man that lives just to fight, in order to shows to the others that he's "the best fighter". He wants to find the real meaning of the beastmen, the reason why Lordgenome created them. Lordgenome explains the truth to him before his death.
Seven years after the disfacted of Teppelin and the end of
Lordgemone, Viral is the only Beastman and the only fighter that tries to protect who decided to live in the subsoil even if Simon and the others made all the population of the world free from the obligations of Lordgenome.
Viral is arrested and brought in prison.
When Simon is betrayed by Rossiu, he meets him in prison and there Viral is ready to fight again, because he's very
nauseous by Simon's behavior.
Viral is a sincere and cruel person that always says what's in his thoughts, and he's fearless to hurt the others.
Simon understands that accepting passively the decisions of Rossiu and the new governament is his worst choise, and thanks to the time spent
discussing with Viral, he finds himself again, and also, the desire to fight.
When Messenger Nia explains that the Moon would collapsed into the Earth just in one mounth,
Rossiu, the new head of the gouvernament, decides to leave the Earth in order to save the major part of the humans he can, knowing that the explosion had to destruct not just the surface of the Earth, but the subsoil too.
It had impossibile to save all the humans, but he prefered to keep the best decision to all deciding to save the savable, even if Simon, Kittan and the others didn't agree.
All the people try to escape into the Arc-Gurren created by Rossiu, but making it, the guards leave Viral and Simon in prison alone, handcuffed and prisoners.
In the time spent together they think that that days could be the last ones spent alive, but Yoko be them free and opens again (again, and again XDDD) Simon's eyes, that finally decides to fight one more time.
He nominates Viral as pilot of the Gurren Lagann, and the scene in which they fight togher kickin' Anti-Spiral's ass is epic!!
So this is the born of a new marvelous duo.
Viral and Simon fight together for the saveness of the Earth and all its population but this NOT means that Viral changed "side".
He isn't an "evil" that becomes "good", simply, he always followed his heart and his ideals, and his desire is to make the beastmen free, so fighting together with Simon he continue to follows his dream, nothing is different.
He isn't the kind of evil that has a fake-pride, rejecting Simon's nominate. He accepts at once making his best.
He's a very smart and strong fighter and his counciles are very precious to Simon, even if their
head-on collision
(and also, their yaoi scenes, that Yoko tries to stop XD), continue to fight.
After the final battle the Earth is safe and Viral can turn back 
home to his population of Beastmen. Other years are spent and he has a beautiful wife and a sweet and adorable daughter.
His smile is sincere, his dream became true.
He becomes Commander of Gurren's troups and he accepts humans even continuing to follow his ideals.
In my personal opinion Viral is the most awesome character of the story, because his development is epic and he's smart, not stupid as opponent and as alliance.
He isn't just a fighter, he desired to live happily and his cute ending is the prove that he wants to be loved, and obviously, he wants to love someone! He has a family!!
The relation between him and Tsuuma (his wife) is better explained in Parallel Works and in the special of the DVD, Viral's Sweet Dream.
Definitely, Viral is a character that is developed at 360°, and a series as Gurren Lagann is the triumph of the hearts of the protagonists, because all of the characters have an important role and a conclusion.
Viral's ending is happy and deserved, surely something so beautiful that we can't forget.
