Unlike most experiments, Manners does not cause mischief. As part of his programming, he is polite to a fault and does not like it when others fight. Thus, he will use his powers to force them be polite and get along. However, he is not mean-spirited and simply wants everyone to be polite and behave.
Experiment 358 was the 358th genetic experiment created by Jumba with Hämsterviel's funding. He was designed to turn people too polite to fight back against bullies. 358 and the other first 624 experiments were deactivated and smuggled to Earth by Jumba during his mission to capture Experiment 626.
All of the experiment pods were released and scattered across the island of Kauai. Against statistically unlikely (but not impossible) odds, several experiment pods landed in one location: Mrs. Hasagawa's yard, 358's pod being one of them.
At an unknown point, Mrs. Hasagawa mistook 358's pod for an apricot and washed it, activating the experiment. However, as 358 was not a very evil or destructive experiment, he was able to live a peaceful life with her, due to the latter seeing the former as a mere stray cat who needed a home.
When Lilo and Stitch discovered that Mrs. Hasagawa kept several experiments as pets, they thought they were a danger to her and, along with Jumba and Pleakley, decided to capture them all. Earlier, 358 politely greeted Lilo and Stitch at Mrs. Hasagawa's door and let them in. Jumba and Pleakley started arguing over who was going to capture 358. Seeing this, the experiment demonstrated his power of making people overly polite on them. Despite Jumba and Pleakley being too polite to capture experiments, 358 was captured anyway by unknown means.
358 and the other experiments were about to be taken away, but were returned to Mrs. Hasagawa when Lilo and Stitch saw how much she cared for them. 358 was then named Manners.
The first 624 experiments, including Manners, were rounded up by Leroy and taken to a stadium to be destroyed. However, Lilo, Stitch, Jumba, Pleakley, Reuben and Gantu arrived before the experiments could be destroyed.
Manners participated in the following battle between the experiments and the Leroy clones, but it is unknown what he did. However, it is presumed that he wouldn't have been able to be very effective, due to the fact that his powers are deemed useless.
The Leroys soon gained the upper hand in the battle, but were defeated when Lilo, Stitch, Reuben and several other experiments performed the song "Aloha ʻOe", which caused the Leroy army to shut down due to the original Leroy's fail-safe.
- The first time Manners' spines appear when he bows, they are yellow; then when the scene changes to where he is beside the door, his spikes are black.
- Like Reuben, Manners is one of the very few known experiments that can speak fluently.
- Manners is one of the few experiments to not appear in the group photo at the end of Leroy & Stitch.