The following are some vague ideas I had while playing Kiwami.
Setting: The setting of Toukiden is great. However, although the levels are a lot of visual eye candy, I feel that they don't have much of an effect on battles. A comparison could be made in this regard to Monster Hunter 4U. In that game, ledges are extremely important for being able to mount monsters. There are also terrain hazards and certain levels which require you to have some form of heat or cold resistance. Some levels also have certain quirks such as wyvern eggs that you can pick up to attract monsters or lava spouts which erupt to damage you. I feel that introducing some kind of level variation or stage mechanics would add more variety to Toukiden.
As far as the overall setting of the game, I feel like Toukiden Kiwami really heavily fleshed out Japanese history. It's true that they could return to Japan and still find more mitama to include, vary up the levels a bit, etc. However, I think it would be interesting if the next game took place somewhere else, such as China.
If they were to make a Toukiden in China, here's how I'd divide the chronology personally. One suggestion I'd make is to differentiate between the high rank and lower rank mitama.
- [+] Spoiler
- Classical Age: Spring and Autumn and Warring States mitama. This would include a lot of the philosophers that make China famous such as Confucius, Mozi and Zhuangzi. However, it would also include military or political figures such as Guan Zhong and Qin Shihuangdi.
High Rank Classical Age: This would include figures from both Han dynasties.
Age of Division: This would include figures from the Late-Han civil war (i.e. Yuan Shao, Yuan Shu, Zhang Lu, etc.) and early "Three Kingdoms" figures (e.g. Cao Cao, Liu Bei, Sun Jian, Sun Ce, Sun Quan, etc.).
High Rank Age of Division: This would first of all include figures from the late Three Kingdoms era and Jin (e.g. the Sima family, Deng Ai, Jiang Wei, Lu Kang). Secondly, it would contain figures from the wars that occurred in between the Jin dynasty and the Sui dynasty (e.g. Huan Wen, Murong Chui, Pei Songzhi, Liang Wudi).
Golden Age: This would contain figures from the Sui and Tang dynasties. It might contain a few from the civil war that occurred after the Tang dynasty as well.
High Rank Golden Age: This would contain figures from the Northern and Southern Song dynasties. It might contain some figures from the Jurchen Jin dynasty, Xi Xia, Liao and others as well.
Age of Conquest: This would contain figures from the Mongols and Yuan dynasty. It might include some from the civil war that ended the Yuan dynasty as well.
High Rank Age of Conquest: This would include figures from the Ming dynasty.
The Last Age: This would include the diehard Ming loyalists such as Koxinga and the early figures of the Qing dynasty.
High Rank Last Age: This would include the major figures of the late-Qing dynasty when it was starting to seriously decline (opium wars, taiping rebellion, etc.).
For equipment, I think they should make it so that if you have 2 pieces of a set, you get a small boost. If you get all 4 pieces, you can get a larger boost. This would allow for a bit more customization of equipment. I think they should work on the equipment aesthetics as well, and possibly add in a bit of fanservice. There should be equipment sets that can make you look similar to the famous figures of other Koei games.
For mitama, I think they should add a mitama fusion system where you can fuse two different mitama and get a hybrid mitama with active skills from two different types (e.g. one attack mitama skill and two speed mitama skills). Mitama fusion could be a good way to get super powerful or rare mitama as well as to customize mitama more to your liking.
To compensate for the power boost given to the player with these things, I think they should make mitama start out weaker. Specifically, I think they should start out with less active skill stocks. You could get mitama with more skill stocks as you unlocked more through acquisition or fusion.
Those are some of the ideas I've had thus far.