The following three skills are the only ones that can go up to level 4: Greed, Acclaim, and Master. They must be unlocked by completing special missions in Survival Mode with a character who has the corresponding skill at level 3. If you have enough money, start from 51F and play until you reach 71F to unlock Greed 4, 86F to unlock Acclaim 4 and 96F to unlock Master 4. Unlock the following level 4 skills by performing the corresponding tasks:
Greed 4 Play the "Great Tournament" mission on 71F. On the first floor, complete a random mission. Then, on the second floor, defeat three generic officers. The field is completely filled with riflemen. Avoid them and defeat the officers. Also, you should use a Resilience 3 skill so that the gunshots don't stagger you. On the third floor, defeat three generic officers again, but the field is filled with Sky Ninjas and Wind Ninjas. Avoid the ninjas and defeat the officers. On the fourth floor, you will face five generic officers in one-on-one battles. They will get progressively stronger and more difficult. When you defeat the final opponent, you will be rewarded with four rice balls that restore your life meter. The fifth and final floor is exactly the same as the fourth floor, but you will face unique generals instead. Once you defeat your final opponent, you will be given two choices: either defeat the last two generals you faced in a special three-way battle to get a bonus, or leave the field. It is recommended to leave if your character is too weak to fight more. You will still get Greed 4 if you leave without defeating your two enemies. After completing the mission, Greed 4 will be available in the shop.
Acclaim 4 Play the "Tutor Wanted" mission on 86F. On the first floor, defeat Tokichiro Kinoshita, a hyper generic peasant, in five battles. On the second floor, you will face Tokichiro again--this time accompanied by a peasant army. Tokichiro will be in Hyper mode, but is still easy to defeat. The third floor is exactly the same as the second floor, but Tokichiro has new bodyguards, such as Nene. On the fourth floor, Tokichiro has turned into Hideyoshi Hashiba and is now stronger and in Hyper mode, along with new bodyguards like Mitsunari Ishida. On the fifth and final floor, Hideyoshi Hashiba is now Hideyoshi Toyotomi and becomes even stronger and more difficult than before. He also has new bodyguards, including Ginchiyo Tachibana, Masamune Date and Yukimura Sanada.
Master 4 Play the "Beyond All Limits" mission on 96F. All the floors have bonus time, which means that every hit will earn gold. Also, each floor has two unique generals, which means that you will face your opponents in two-on-one battles. On the first floor, defeat Kenshin Uesugi and Shingen Takeda. On the second floor, defeat Ginchiyo Tachibana and Nene. On the third floor, defeat Kotaro Fuma and Kojiro Sasaki. On the fourth floor, defeat Hanzo Hattori and Ieyasu Tokugawa. On the fifth and final floor, defeat Yukimura Sanada and Mitsunari Ishida.