You can earn a level 5 weapon on any difficulty setting:
Hanzou Hattori
Weapon: Night Fang "Underworld"
Stats: Base Attack 46, Night Element, Musou +40, Ranged Attack +45, Movement +42, Jump +32
In the battle of Mikatagahara, the general objective is to withstand the Takeda army's battle formation. Once the stage starts, lure Naitou Toyomasa and Yamagata Masakage forward and defeat them. Then, defeat Oyamada Nobushige and immediately move towards Baba Nobufusa's location. Defeat him without letting Hirote Hirohide get defeated. Anayama Nobukimi and Takeda Katsuyori will come towards you; defeat them as well. You cannot allow any of your allies be defeated. Infiltrate the enemy camp using the ninja route, then take all the enemy gates and the supply team will appear. They appear slightly to the east of your home camp and move west. Defeat the captain for the weapon. Shingen will start retreating once you take all of the gates. It may be prudent to wait until your allies are close to his camp before taking the last gate to get in his way.
Keiji Maeda
Weapon: Jeweled Halberd of Heaven
Stats: Base Attack 50, Lightning Element, Life +50, Attack +46, Mounted Attack +44, Musou Gain +25
In the Test of Kawanakajima defeat all enemy generals and subgenerals except for the commander. The supply team will show up in the southwest and move towards the north exit point. Defeat the captain for the weapon.
Kunoichi
Weapon: Kushinada
Stats: Base Attack +45, Ice Element, Life +37, Musou +45, Ranged Defense +49, Jump +29
Kunoichi's weapon is very easy to get, because you do not have to kill anyone.. In the Rescue Of Ueda Castle, reach the fifth floor in less than three minutes without defeating any enemies. A precious item report will appear. Go to the northwest, and the weapon will be in one of the rooms there.
Masamune Date
Weapon: Periwinkle "Mikaboshi"
Stats: Base Attack 46, Ice Element, Attack +45, Mounted Attack +35, Musou Gain +32, Attack Radius +39
In the Intrusion of Honnouji, arrive at the temple before Mitsuhide. Defeat Mitsuhide's generals, then defeat Mitsuhide himself. Next, defeat all of Nobunaga's generals and subgenerals. Complete all this without any of your own generals having lost and the supply team will appear in the temple, running for Nobunaga's exit point. Defeat the captain to pick up the weapon.
Mitsuhide Akechi
Weapon: Sacred Sword "Futsumitama"
Stats: Base Attack 47, Lightning Element, Attack +42, Musou +37, Defense +46, Attack Radius +28
In the Battle of Yamazaki upper version, first defeat Nakamura Kazuuji and the guard captains on Tennouzan . A mission will appear to assist Matsuda Masachika towards the south. Do so by defeating Nakagawa Kiyohide and Takayama Shigetomo. Next, clear the Tennouzan of enemies quickly before the Maeda Keiji charge or enemy reinforcements events show up about five minutes into the battle. If you do so, a supply team will appear near the enemy commander, heading towards the cave up north. Defeat the captain for the weapon. Note: You cannot let your guard captains on the Tennouzan die.
Nobunaga Oda
Weapon: Aramasa of Orochi
Stats: Base Attack 48, Night Element, Musou +45, Attack +26, Mounted Attack +49, Attack Radius +35
In the Battle of Okehazama, defeat the two front-line guards of the Imagawa army. A mission will appear to assist Hideyoshi. Ignore it and let him be defeated. Next, defeat Imagawa's generals until he has two remaining. Hanzou will show up and run towards the enemy base as support. Get to the base first and the supply team will appear near the southwest, near Hideyoshi's original location. Defeat the captain for the weapon. Hanzou is extremely fast. You will probably require a horse (preferably Matsukaze).
Yukimura Sanada
Weapon: Fire Lance "Susanoo"
Stats: Base Attack 47, , Fire element, Life +50, Musuo+27, Attack+48, Defense+38
Defeat 1,000 enemies in the Summer campaign of Osaka. Clear the following missions: Luring the two generals in front of your cannons, returning to home base, and preventing Masamune Date from entering the castle. At this point, the mission to charge into the enemy camp will appear. Take this opportunity to defeat as many enemy generals as possible and build your kill count. Then, charge into the enemy camp and continue towards 1,000 opponents. A supply team will appear near the southwest of the map and move towards the east gate of the castle. Defeat the captain for the weapon.