lonely personality;
The personalities found in Xenosaga are highly based upon various Enneagram types. In fact, the Official Design Materials for Episode I classifies the characters in these groups. Enneagram types are typically discerned only through self-observation, unlike other personality types like the western and Eastern zodiacs, and blood-type systems that are typically used in games. There are nine distinct types. In real life, each person has different branches into other types. However, in the case of Xenosaga, they tend to list the characters as strictly one type. Some of the characters are also sometimes listed differently than they should be. However, in Ziggy's case, I feel this is pretty accurate.
Type Nine
Ziggy is listed as a type nine, which can be described as a "Mediator, Peacemaker, Preservationist". . At their best they are perceptive, receptive, gentle, calming and at peace with the world. However, in Ziggy's case, he is far from being at his best. Ziggy is actually an extremely unhealthy type nine. At this level, Ziggy is extremely self-destructive. He wants to disassociate himself from reality. His main desire when we first meet him is to become completely robotic, erasing every last bit of his humanity that was left.
The main reason why Ziggy acts this way is because he lives with a great amount of grief and sorrow over his failures as a human. When he committed suicide, he did so because he had nothing left to loose. He couldn't prevent his father from being killed, or his mother from dying, and he couldn't save his family. Instead of joining Voyager as a Testament, or choosing to continue to exist in his brain as just a consciousness, he took his own life.
However, two years later, he was revived as a cyborg without consent. He was also implanted with a program which prevents him from taking his life again. Furthermore, under the Life Recycling Act, he has no human rights, and no control over his life or death. Additionally, he prefers to take missions that are extremely dangerous, in hopes that he will somehow die in the process. However, due to all of this counter programming, he's able to escape danger and survive. Realizing that these methods were futile, he seeks to replace every last part of him with mechanical parts--to become a robot. It's an extremely slow process, but it's the only way he can try to gain some control, and make the painful memories of his family go away.
What is so interesting about Ziggy is that like other characters in the series, the Testaments, and Yuriev, Ziggy seeks to loose his humanity because he lost faith in his ability to live as a human. However, instead of seeking to become more powerful to gain control, he chooses to erase himself completely.
Winds of Change
Ziggy's personality goes through a series of changes throughout the course of the series. At first, he asks Juli Mizrahi to erase the memories of his human life as compensation for retrieving MOMO. However, upon meeting her, MOMO begins to remind him of his stepson, Joaquin. Also, in many ways, she also reminds him of himself when he was younger.
As he begins to travel with MOMO, Shion, and the others, he slowly starts to become less like a machine, but ever so slightly, more human. For the first time since he had become a cyborg, he begins to develop relationships and connections with others, peticularly with MOMO and Jr. The others in the party begin to rely on him for strength and support. Little by little, his destructive behaviors begin to subside.
In Episode II, Ziggy gets a good deal of development. When we first see him, he tells Jr that he has no intent on "prolonging things". He has a conversation with Juli, and asks her to consider MOMO as another daughter instead of a copy of Sakura. At first, I feel that Ziggy does this because although he does care about MOMO's well-being, he is still fixated on ending his life.
However, during MOMO's analysis, and her destruction of her mind, he has flashbacks of loosing his stepson and wife. Not wanting to live through that kind of pain again, he shows a lot of determination when going into her subconscious domain to try and save her.
After MOMO is saved, we don't see Ziggy again until a bit of time. As you play Shion wandering around the remodeled Elsa, you can see Ziggy and MOMO engaged in a conversation.
Near the ending, when Ziggy is confronted again by Voyager, he goes into a fit of rage--something that none of the other characters had witnessed from him. Then, he punches through the wall in order to save everyone. In the process he looses his mechanical arm. MOMO stays by Ziggy's side and repairs him. At this point, Juli asks if he'll consider living just a little while longer for MOMO's sake, and her's as well.
I think his choice to remain alive was that MOMO reminded him of his own situation. He realizes that he's the closest thing to a father figure that she might ever get a chance to know personally. Beyond that, realizing that Voyager was still around must have made a very large impact on his decision. During the credits, he tells MOMO and Juli that he's decided to go through life extension. Although Juli and MOMO are going to Fifth Jerusalem to live, Jr offered to "take him in" so that he would be able to see MOMO again.
The Ending
Although entirely optional, his swimsuit is a bit interesting aside from the design, in that it's clearly a realian body. Although the database states that Ziggy chooses to remain in his cyborg body, it could be possible that he would transfer into this one from time to time, for whatever reason.
One of the most memorable scenes in Xenosaga 3, at least for me, is when Canaan tricks Voyager in order to put a stop to him. Although it he doesn't show it as much as other characters, you can easily tell how upset he is upon realizing Canaan's identity, his purpose, and his last message to him. Beyond just writing, the voice actors also did a very good job at portraying the emotion in his voice.
By the end of the game, it seems that Ziggy has come completely full-circle. Instead of wanting to end his life, he seems to embrace it, and treasure every moment that he can with MOMO and Juli... perhaps as a new family. He no longer wants to erase his memories, but he realizes that through all of the pain he had suffered, it was these memories which made him human. He learns to accept them.