When you reach Genin level 20, you will no longer gain EXP from missions. To remove that limitation, you have to pass the Chunin Exam. Complete the campaign and you will be awarded the rank Chunin and unlock pet shop and use pets.
Chunin Exam 1/5: Written Test
The first round will be a written test. Answer the questions correctly to proceed to the next round. There will be five questions. The questions are easy so you don't have to use tokens to see the correct answer. Refer to the list of questions below. Answers are given at the end.
1. Which actions allow you to gain chakra in battle? - Charge
2. What was the first weapon that Shin gave you? - Kunai
3. How many friends can you recruit to join your party for missions - Two (2)
4. Which technique is specialized in illusions and transformations? - Genjutsu
5. Which item allows the character to recover HP? - HP Healing Scroll
Chunin Exam 2/5: Scroll War
Your main objective is to collect 2 scrolls. You will encounter enemies along the way. Defeat them to obtain the scrolls. Recruit 2 friends to finish this stage easily.
Chunin Exam 3/5: Arena
This stage will be a 1vs1 battle. You cannot recruit friends to help you. Arrange your jutsu for PVP and bring in some healing scrolls. First opponent - Lok Li, a ninja expert on taijutsu. Lok Li has a stunning skill. Second opponent - Shira, has control on bugs and insects. Shira can burn your chakra. Third opponent - Zuka, who can tame animals. It hurts you know when two opponents attack you.
Chunin Exam 4/5: Team Battle
This is suppose to be the Final Exam. But Kojima interrupted the event. A ninja named Ken was kidnapped and you have to save him. But 3 ninjas from the Earth village will block you from chasing Kojima so your team will have to fight them. Objective: Defeat the earth village ninjas. Recruit 2 team mates to join the battle. Read this: Cheat recruit members.
Chunin Exam 5/5: Final
Arrest Kojima and bring Ken back.
Congratulations! You have passed the exam! Back in 2010, this campaign is so difficult to pass.