Originally, Janine's goal was to use Poison-type Pokémon just as well as her father. After becoming a Gym Leader, Janine hopes that by applying herself, she'll improve her skills and become better than both her father and (following her loss) the protagonist.
When encountered in her Gym, Janine hides behind the invisible walls that were installed prior to Generation I/III. To further confuse her challengers, the junior Trainers of the Gym are disguised like Janine. Once they have been defeated, the Leader will battle with a team of Poison-type Pokémon. Once defeated, she will yield the Soul Badge and a Poison-type TM: TM06 (Toxic) in Generation II; TM84 (Poison Jab) in Generation IV.
Like the other Gym Leaders of Kanto and Johto, Janine will leave her Gym from time to time in HeartGold and SoulSilver. Every evening between 4:00 PM and 6:00 PM, she can be found at the Pokémon League Reception Gate near Victory Road, on her way to visit her father and deliver his lunch (from 6:00 PM to 8:00 PM, she will say she is done delivering the lunch and offer to take a photograph with the player). She will give travelers her phone number, after which she can be called on Monday afternoons to arrange a rematch at Saffron City's Fighting Dojo. On Mondays, she can be found in the Celadon Department Store arguing with Falkner over which of their fathers is the superior Trainer.
Before the events that led to her employment as the Gym Leader, Janine hung around outside the Fuchsia Zoo. She will tell the protagonist of Pokémon FireRed and LeafGreen that Koga is teaching her how to use Poison Pokémon in an obvious reference to the previously released Generation II games.
Janine also appears in Pokémon Stadium 2's Kanto Gym Leader Castle. This is the only time in which her active team contains Pokémon not of the Poison-type. Despite this, all her Pokémon in Round 1 know Toxic, a Poison-type move and the TM she gives in the Generation II games.
"I'm on my way to my dad's house to give him his lunch. The Elite Four has no time to rest, day or night. It's such hard work, you know? Say! Do you want to exchange numbers?"
Yes: "Call me on Monday around noon if you want to battle!"
No: "You don't look like you're scared, but you are, aren't you?"
"Now you want to know my number, don't you?"
"Hello, hello, hello... Oh, hello, what are you up to? I'm just fine, thanks! Many of the Gym Leaders are much stronger than I am. We've just got to work harder!"
"Hello, hello, hello... Oh, hello, what are you up to? I'm just fine, thanks! My schedule's fairly open on Monday afternoons. Would you mind calling me back then?"
"Sorry? I’m afraid I can’t hear you very well. Must be a bad connection. Can you call again from somewhere else?"
Her calling the player
"This is Janine. How are you doing? Hey, can I talk to you about my dad? Only if you want to hear, though. Seriously? I might talk your ear off if I’m not careful!"
"This is Janine. How are you doing? See, I’ve been training with my dad since I was little--to be a Gym Leader. I haven’t even considered taking any other path, really. It’s my dream to someday become a better Gym Leader than Dad!"
"This is Janine. How are you doing? Falkner in Violet City... He’s talking about his dad all the time! Seriously, he’s such a daddy’s boy, he needs to become his own person sometime, you know? What do you mean, I should talk? Ha ha--mind your own business!"
Janine debuted in Crossing Crobat. She was first seen on a mission where she helped test the security of Goldenrod Museum by pretending to steal a Big Pearl. After completing the mission, Janine left to ponder what she was doing with her life. Her father, Koga, had served under Giovanni as both a ninja and a member of Team Rocket. Koga had intended on having Janine join Team Rocket as well when proper time came, but he eventually disappeared after Team Rocket's defeat, leaving Janine alone without anyone to guide her.
Shortly after, Janine was attacked by Suicune, the Legendary Pokémon that had been attacking various other Gym Leaders around Johto. Hoping that if she managed to capture it, her father would hear about it and return, Janine faced Suicune battle. Though she proved to be a powerful opponent with her variety of ninja techniques, Janine was eventually defeated by Suicune. As Suicune began to leave, Janine realized the reason it was challenging the Gym Leaders was to find a proper Trainer who could command in battle. Finding herself to in a similar situation of not having a master, Janine told Suicune she wished to challenge it again in the future before both went their separate ways.
In Yikes, It's Yanma!, Janine participated in an exhibition tournament between the Kanto and Johto Gym Leaders. During the tournament, she was paired up against Falkner. In Notorious Noctowl, Janine and Falkner began their battle against each other. While both participants used a variety of skills against each other, Janine chose to forfeit the battle in order to pursue what she thought she was her father in the crowd.
In Lugia and Ho-Oh on the Loose (Part 1), Janine joined the Kanto and Johto Gym Leaders in helping fend off the Masked Man's army of mind-controlled Team Rocket Grunts from attacking the Indigo Plateau. As they fought, Janine and the Gym Leaders were led onto the Magnet Train, which the Grunts had used to infiltrate the area. After they got on, the Magnet Train sped away from the area as part of the Masked Man's plot to prevent the Gym Leaders from interfering with his plans. In The Last Battle IX, the Magnet Train was stopped by Red, preventing it from crashing.
Ariados is Janine's first known Pokémon. He was first seen being used to help Janine break into the Goldenrod Museum. Later, he was used to battle against Falkner during the Gym Leader exhibition tournament. Using its powerful thread, it managed to bind Falkner's Noctowl, forcing him to switch for his Skarmory. By using its abdomen, Ariados can produce a thread used for defensive techniques, such as Spider Web, while the thread shot from its mouth is sharp enough to pierce even metal with enough time.
Weezing is Janine's second known Pokémon. It was first used to break into the Goldenrod Museum. By using its gas, Weezing created a smokescreen that exposed the security beams, allowing Janine to easily navigate past them.
Forretress is Janine's third known Pokémon. It was first used to attack a group of security guards at the Goldenrod Museum. By using Spikes as caltrops, the guards were unable to pursue Janine after she obtained the Big Pearl.
Crobat is Janine's fourth known Pokémon. It was first used to battle against Suicune. With its speed and Double Team, Crobat and Janine made it hard for Suicune to track them. Eventually, Suicune won after using the moonlight to expose Crobat and Janine's shadows, allowing to figure out which copy was real.
Grimer is Janine's fifth known Pokémon. It was first used to battle Falkner in the Gym Leader exhibition tournament. Using its Minimize, Grimer shrunk down so that Falkner's Noctowl couldn't track it, allowing to attack unnoticed. It was eventually defeated after Noctowl used Foresight to find it, forcing Janine to switch it with Ariados.
Janine's Pokémon Cards listed with a blue background are only legal to use in the current Expanded format. Cards listed with a silver background are legal to use in both the current Standard and Expanded formats.
In the Generation II games, Janine's whole Pokémon team is the opposite gender to her, despite the 50-50 gender ratio. This was changed in HeartGold and SoulSilver, in which she has an all female team rather than an all male team like before.
In the English versions of the Generation II games, there is a grammatical error in the sentence where she gives the Soul Badge to the player. This was corrected in the remakes.
Janine, along with Erika, are the only Kanto Gym Leaders to give the player a TM upon their defeat in Gold, Silver, and Crystal.