Back on Earth, Keiji Onizuka was a world class boxer. He was the champion and everything seemed to be perfect in his life. Even his manager suggested that if he had a sick mom it would add more drama to his story. Well, he did. Every week he would take the last ferry to the island where she lived and spent the weekend caring for her. One day, he noticed his retina had started detaching, which meant he had to stop boxing. He had to give up doing the only thing he knew how to do, fight. Keiji decided to stay on the island and get a regular job as a delivery boy even after his mother passed away from her illness. There was no other meaning to his life anymore.

When U-NASA sends him an invitation, he refuses at first, but the words of his late mother ring in his mind telling him to move on and find a life. When he finally agrees to go for the MO surgery, he requests one with the best eyesight. Why? Because he wanted to be able to see the island his mother lived in from anywhere. He just wanted to make his mom proud and show her he had friends and found a new reason to live. While not the saddest of them, Keiji's story is a good warm-up for what's coming up on the list.

The main protagonist of the show must, of course, have a backstory that tugs at your heartstrings. Akari grew up in an orphanage and his best friend Yukari is plagued with the AE virus that has spread on Earth and an organ transplant is supposed to be the only cure. But that's expensive, so what does a big, strong twenty-something man with special strengths do? Well participating in cage fights for the filthy rich, of course!

Yukari is losing hope and lashes out at him constantly, but he's found a donor in a foreign country! Except it wasn't true. After barely surviving a match against a grisly bear, he's told Yuriko died and there was never a donor. She was all he had in his life, and truly loved her, except he never actually said it to her face. Now he has a motivation to help cure those with the same disease by getting the Mosaic Organ Operation and going to Mars.

Now the leader of the Japanese and American squad, Shokichi has a painful past. When he was 15 years old he saw his best friend, Nanao Akita, being abused by her stepfather, as he often did. Enraged, he attacked and killed him to save Nanao. When they were both 22, Shokichi underwent the surgery to follow Nanao on the BUGS 2 mission, after which they wanted to live a peaceful life together.

On their arrival, the two encounter a cockroach and peaceful Nanao convinces Shokichi to talk to it instead of attacking. In the blink of an eye, the girl Shokichi loves and has dedicated his life to protecting has her neck snapped by the Martian and collapses. With her final breath, she asks him not to transform because she doesn't want to see him being violent like when he killed her stepfather. And he complies. After all of his efforts to keep her safe, his best friend and beloved was taken from him in a second. He later refers to his dead friend when recruiting Akari, as they both have lost someone thanks to these creatures. And during the Annex 1 mission, another girl who loved him dies in his arms. This poor guy can't catch a break!

Like so many others in the BUGS and Annex missions, Thien grew up as a poor child. He has stated that he is from the poorest background on the mission. He grew up in Thailand and had a best friend named Ploy. When they were 10 years old, Ploy got taken away to “work” in the city. When Thien realized that she had been sold into prostitution, he went looking for her in the city.

After much searching and asking, he finally found out she had been disposed of because she had become “infected”. He spent the rest of his time before joining the BUGS 2 mission living on the city streets.
When the entire team gets attacked and overpowered by the roaches, he overdoses on the drug to save Ichiro. The overdose causes his human form to literally fall apart as he transforms into a giant locust before dying. With his last breath, he tells Ichiro and Shokichi that he has grown to like them because of their will to live, which a cold insect-like man like him never had.

While growing up, Ichiro was the oldest of eleven kids and had a sick mother. Her only wish was for Ichiro to go to Tokyo University so that he could get a prestigious job. Ichiro was a hardworking student and all was going well until a teacher he trusted blackmailed him after a student he was having an affair with became pregnant, forcing Ichiro to take the blame for “forcing himself on her” and getting her pregnant.

All he wanted was to make a good living to support his ill mom and siblings, but this betrayal would cost him everything and he'd never trust anyone again. This desperate need for money is what drove him to become part of the BUGS 2 crew and risk his life with the rest of them. However, Ichiro's sad story has a happy ending. He's one of the two survivors of that mission and he managed to become the 502nd Prime Minister of Japan!

Wolf Redfield was an IT guy at his American company. He worked day in and day out without rest and was always by himself. The day before his wedding, he also had a very important deadline to meet and he worked harder than ever to do it on time. In the wee hours of the day he was supposed to get married, the program he was working on bugged out, but left it as it was so he could make it to his wedding.

He was still late and his bride was pissed. His boss found out about the bug and tore him a new one. The stress was such that he got sick and quit his job. His marriage immediately broke apart, he got divorced and was all alone. Thanks to his amazing technical abilities, he was recruited for the Annex 1 mission as a non-combatant like the rest of the “nerds” in their group, giving him not only a group of friends for the first time but also the possibility of a big paycheck if he makes it back to Earth.

Alexander Asimov grew up as an orphan. Once he was old enough he joined the army and then fell in love at first sight with Gina S. Asimov. Gina rejected him repeatedly, but he could see himself building a family with her so he didn't give up. He stalked her daily but Gina knew her father wouldn't approve. Her father being Sylvester Asimov, a.k.a. “the invincible war god”. Alex's first meeting with Sylvester started with a punch to the face and that was the case every time after that. Gina softened up and gave Alexander makeovers to try and make him look like someone her father would approve of, with little to no success. Finally, Alexander won Gina's heart with his dedication and Sylvester eventually gave Alexander a chance. The two got married and pretty soon, Gina was pregnant. Alexander couldn't believe he finally had the family he'd never had. For once, things were looking up.

But it was too good to be true. Gina and their unborn son were hospitalized with the AE virus. The only solution was for Sylvester to betray his past allies to find a vaccine, which he'd gladly do for his daughter and Alexander, who he now considered his son. Of course, Alexander joins him and they both head to Mars to save Gina and the baby.

During a battle against the Chinese traitors, Alexander loses an arm to a Terra Formar and then faces off with the Chinese team who overpower him, which leads him to overdose on the drug, transforming into a giant stag beetle. Alexander dies swearing he'll get the vaccine for his family. Of course, he died for nothing.

Sheila was raised in Mexico and was the daughter of a wealthy family. Marcos Garcia and Alex Stewart were two boys who worked for her family and lived in their care. She grew up with both of them and they became so close that she helped them stop getting into fights. They were as close as siblings. Until the workers rioted and her father committed suicide. They lost everything and became separated. Sheila and her mother fled towards America, where she eventually became a US citizen, though her mother didn't survive. Sheila even mentions that the 36% survival rate of the MO operation is a better chance of survival than staying in Grand Mexico.

Once on the mission, Sheila falls in love with Shokichi. She learns Japanese during the 39 day-long trip to Mars from Akari so she can talk with and get closer to Shokichi and got him to teach her how to use the net gun. During a surprise attack from the Terra Formars, Sheila is able to immobilize one of them, but it shoots her in the chest. Shokichi picks her up as Marcos crushes its head. Sheila grabs on to Shokichi's collar and attempts to confess her feelings, however, it's impossible with a gaping hole in her chest. In the end, she dies staring into Shokichi's eyes trying to say “I love you”.

Hong is a young teenage girl in the Chinese team. She is a non-combatant and was only chosen to join the Annex 1 mission to Mars thanks to her affinity for the Bacteria MO operation. She has the powers of a lethal bacteria, making her a biological weapon that can kill anybody without a protective suit. This poor girl was basically taken from her poor family and sent to Mars at around the age of 15, on top of that, must expose herself in order to use her ability and release the deadly bacteria from her body. That in itself is already kind of a bummer, but there's more.

She is a kind, innocent, peace-loving girl who's never wanted to harm a living being, especially a human. But being a part of Division 4, she is forced to kill her own kind at the orders of Liu Yiwu. She's just a scared little girl pulled into a war and used as a weapon who hates to see those around her die, not to mention being responsible for their deaths. To top this all off, like the rest of Division 4, she has no hope for a normal life once she returns to Earth, since spending any time in a room with her would be detrimental to any living being. And she's still just a kid!

Adolf and his parents joined the BUGS2 project in Germany when he was only 7. His parents didn't survive the surgery, so he alone became a lab rat for the MO operation. He was poked, prodded and sliced after he volunteered to save the other kids he was held with. His surgery was successful, but not without side effects. His base is the electric eel but his human body couldn't handle the electric current and was burned and destroyed through countless experiments, leaving him permanently scarred and disfigured. To counter this, he had grounding devices implanted, which meant not only more surgeries, but more excruciating experiments.

While being allowed to attend school, all he wanted was a way to run away from the military and die. Until he fell in love with Rosa, who was kind to him and went out of her way to get close to him. She made him feel human again and they eventually got married and were happy. Until his wife cheated on him because she “felt lonely and was weak”. Of course, Adolf forgave her. Later they had a baby, but when they checked it to see if it had inherited Adolf's MO, they realized the baby wasn't his. His wife then left him.

Once on Mars, constantly haunted by these painful memories, he once again only wished he could die. And after defeating a vast number of the Terra Formars singlehandedly, his subordinates come to his rescue as he had so many times been there for them. He was so worn down already, he could do nothing but watch them get destroyed by the monsters. This gave him back his will to live, at which point he overdosed on the drug just to save his men, who he saw being taken away by the enemy regardless. The Terra Formars that were left decided to finish him and Eva off by stoning them. Adolf protected Eva with his body and then finally died. Adolf's story is by far THE most tragic one we've seen so far in this show.