How can I unlock these four characters?

[⎝⧹Za Furan⧸⎠]

I have finished all campaigns in Story Mode.

http://oi68.tinypic.com/m08cj.jpg

[Netflix]

Haven't clicked on the link, but I know that at least four of the characters are unlocked through Challenge modes.

I recall getting:
Imagawa
Musashi
Kojiro
Okuni

from clearing the Survival, Gold collecting, Speed and Chaos mode

[Doomvora]

Scroll to the bottom if you want your answer right away.

Originally posted by GameFAQs:

Unlocks in Free mode - characters are unlocked as you clear the stages they are playable in. Therefore, the characters you unlock depend on the order of the stories you complete.

Akechi Mitsuhide// Clear Oda Story Chapter 2
Aya// Clear Uesugi Story Chapter 1
Azai Nagamasa// Clear Azai Story Chapter 1 or Oda Story Chapter 2
Chosokabe Motochika// Clear Chosokabe Story Chapter 1 or Oda Story Chapter 8
Date Masamune// Clear Date Story Chapter 1
Fukushima Masanori// Clear Unification Story Chapter 1
Fuma Kotaro// Initially avaliable
Gracia// Clear Chosokabe Story Chapter 1 or Oda Story Chapter 8
Hattori Hanzo// Clear Tokugawa Story Chapter 1
Hojo Ujiyasu// Initially avaliable
Honda Tadakatsu// Clear Tokugawa Story Chapter 1
Ii Naotora// Clear Tokugawa Story Chapter 1 or Hojo Story Chapter 2
Imagawa Yoshimoto// Clear Tokugawa Story Chapter 1
Ina// Clear Tokugawa Story Chapter 2
Ishida Mitsunari// Clear Sekigahara Story Chapter 1
Ishikawa Goemon// Clear 1st Mission of Mercenary Mode
Kai// Initially avaliable
Katakura Kojuro// Clear Date Story Chapter 1
Kato Kiyomasa// Clear Sekigahara Story Chapter 1
Kobayakawa Takakage// Initially avaliable
Koshosho// Clear Chosokabe Story Chapter 1 or Oda Story Chapter 8
Kunoichi// Initially avaliable
Kuroda Kanbei// Clear Oda Story Chapter 4
Lady Hayakawa// Initially avaliable
Maeda Keiji// Initially avaliable
Maeda Toshiie// Initially avaliable
Matsunaga Hisahide// Clear Oda Story Chapter 3
Miyamoto Musashi// Clear 2nd Mission of Mercenary Mode
Mori Motonari// Initially avaliable
Mori Ranmaru// Clear Oda Story Chapter 4
Naoe Kanetsugu// Clear Uesugi Story Chapter 1
Nene// Clear Oda Story Chapter 2
No// Initially avaliable
Oda Nobunaga// Initially avaliable
Oichi// Initially avaliable
Okuni// Clear 1st Mission of Mercenary Mode
Otani Yoshitsugu// Clear Azai Story Chapter 1
Saika Magoichi// Clear Oda Story Chapter 2 or Date Story Chapter 2,
Sanada Nobuyuki// Initially avaliable
Sanada Yukimura// Initially avaliable
Sasaki Kojiro// Clear 2nd Mission of Mercenary Mode
Shibata Katsuie// Initially avaliable
Shima Sakon// Initially avaliable
Shimazu Toyohisa// Clear Shimazu Story Chapter 1
Shimazu Yoshihiro// Clear Shimazu Story Chapter 1
Tachibana Ginchiyo// Clear Sekigahara Story Chapter 5
Tachibana Muneshige// Clear Sekigahara Story Chapter 5
Takeda Shingen// Initially avaliable
Takenaka Hanbei// Clear Oda Story Chapter 3
Todo Takatora// Clear Azai Story Chapter 1
Tokugawa Ieyasu// Clear Tokugawa Story Chapter 1 or Oda Story Chapter 4
Toyotomi Hideyoshi// Initially avaliable
Uesugi Kagekatsu// Clear Uesugi Story Chapter 1
Uesugi Kenshin// Clear Uesugi Story Chapter 1
Yagyu Munenori// Clear Oda Story Chapter 3

Not entirely sure what mercenary mode is though, i assume challenge mode, most likely survival challenge mode.

There is surprisingly little information regarding this and i keep coming across this list.

You're missing Goemon Ishikawa, Yoshimoto Imagawa, Musashi Miyamoto, and Kojiro Sasaki.

Originally posted by The 4 characters you need:

Imagawa Yoshimoto// Clear Tokugawa Story Chapter 1
Ishikawa Goemon// Clear 1st Mission of Mercenary Mode
Miyamoto Musashi// Clear 2nd Mission of Mercenary Mode
Sasaki Kojiro// Clear 2nd Mission of Mercenary Mode

Not sure how you missed Imagawa honestly.

[DeeeFoo]

^ That's for SW4, since it mentions Chronicle Mode. Their unlock methods in 4-II are different.

For 4-II, I think you just do the challenges and the castle in the castle mode.

[kyromaru]

Maybe if you play with different characters you can unlock different events in each stage, MAYBE, i don't know...

[Inochizao]

Thank you guys! You're amazing!

There is another way, less challenger, that i did accidentally:

Buying the DLC Weapon Set. It has unlocked them automatically. I even think that it shall unlock everyone if you buy right at the beginning (i haven't and didn't know).