Chuchu is a Pokémon of Yellow. She is the first female Pikachu and the first one seen to have offspring.
Chuchu was captured about three years after Yellow's first appearance in the Red, Green & Blue chapter. Yellow took it in after she found her injured in the Viridian Forest, and it was seen by her side first in VS. Tyranitar when she introduced it to her uncle Wilton. After noting that it had grown quite attached to her, he expounded on his real objective, which was to ask Yellow to go to the Johto region with him to investigate on Lugia. Because the sheer magnitude of a monster that they're dealing with doesn't leave him with many options alone, he needed someone to go with him, and Yellow came up with the idea to ask Red. After Yellow found him training near the Viridian Forest, Chuchu seemed to take a liking to Pika soon after they met. However, with Red's wrists and ankles still weak from the damage that Lorelei's ice cuffs left on them, he needed to recover at the hot springs of Mt. Silver, and left Pika behind.
Alongside Pika and Yellow, Chuchu flew to Johto on Kitty with Wilton's own Butterfree, where they soon encountered Crystal after the latter mistook Pika for a wild Pokémon. Soon, however, the two trainers got involved in Lugia's rampage and lost consciousness in the shipwreck.
Following the incident, Chuchu and Pika produced an egg when Pika spent time with it in the Johto Daycare Center. When the Masked Man took the three hostage near Ilex Forest, Gold embraced their egg and took a number of blows to guard it, hatching the Pichu that the egg contained. With Pichu's assistance, the boy eventually succeeded in defeating the villain, and Chuchu's offspring was left in his care.
Much later, in the FireRed & LeafGreen chapter, Chuchu was seen with a teenaged (albeit short) Yellow as they visited the Viridian Gym together. On its own will, it challenged the gym and found itself overwhelmed and defeated at the hands of Blue's Alakazam, and after recovering with Yellow's mystical healing power, met up with Silver, who was searching for his roots nearby. Through a chain of events, it then found itself in Red's hands after Yellow spent the last of her energy informing him of Deoxys's message, and assisted in defeating Carr's ten Forretress.
Two months later, it and Pika, who were thankfully able to escape the beam that left their trainers petrified, traveled with Gold and Crystal to the Hoenn region to help save Jirachi. Soon, Gold also revealed that the two and his own Pichu had learned Volt Tackle to help out, and after the remaining five of the Pokédex Holders succeeded in freeing their comrades, the three dealt the finishing blow to Guile Hideout's giant Kyogre monster.