Why does Kishimoto never reveal the true face of Tsunade in Naruto? Personally, I think the main reason is to maintain the appeal to Naruto's fan base, coupled with the fact that the true face of the Tsunade has not been disclosed in order to reflect the strong chakra control ability of the Tsunade, which is explained below.
Most of Naruto's fan base is young men, and Tsunade's ability to maintain the overall popularity of Naruto's work by remaining young can continue to be popular.
Most of the fans of anime works based on fighting are young men, the so-called lady gentleman is good, most of this type of anime will design some female characters who are generally liked by the fan group in terms of appearance conditions, and Naruto is also not exempt from this.
After all, the group watching Naruto is still young men as the main force, in this case, Kishimoto in order to maintain the heat of the work, it is obviously impossible to easily announce the true face of the Tsunade, after all, the role image of the Tsunade is very successful.
It can meet the expectations of most Naruto fans (the design of other female characters in Naruto has similar functions except for Tsunade), and once the true face of Tsunade is revealed, the result is that the number of fans and popularity accumulated will decline significantly.
Originally, the quality of Naruto's plot content was still very strong although the decline in time, if there were no other factors that could maintain fans' attention to Naruto, it was not conducive to maximizing the commercial value and interests of Naruto. In this case, Kishimoto naturally will not easily disclose the true face of Tsunade, so as to avoid further causing further loss of Naruto's main fan base.
The only time Tsunade almost revealed his true face is in the plot after Payne's invasion of Kiba Village, in order to save a large number of villagers and ninjas in Kiba Village who suffered a large number of casualties due to Payne's attack, Tsunade consumed a large amount of his own chakra, and the reason why Tsunade was able to remain young was to use his special ability to accumulate and accurately control Chakra.
As a result, due to the impact of the war, the Tsunade showed a state of fatigue, and in this case, from the plot point of view, the aging state of the Tsunade was forgivable. Anyway, Kishi had concerns that once the true face of the Tsunade appeared, the decline in fan activity and continuous attention was not worth the loss for Kishi, and everyone could see the shape design of the previous popular female characters in the Hirohito Biography to know why the popularity of the Hirohito had fallen sharply.
Another reason why Tsunade's true face did not appear was to reflect the strong ability of Kiba Sannin, all three of whom are characters with skills in the plot.
Naruto in the kiba three ninja occupation of the scene can not be less, in addition to a good ability to set the Tsunade, one of the common characteristics of the Tsunade and the Great Snake Maru is not to show old age, it is difficult to think that he is 50 years old if he does not have a white hair, the reason why the Tsunade and the Great Snake Maru do not appear old is to master special ninjutsu, in fact, the ability comparison between the three ninjas is their own strengths.
Among them, the advantage of the Tsunade is that its Chakra storage ability and the precise control of the use of chakra can maintain their appearance in a young state is the display of the personal ability of the Tsunade, and the peak of the individual ability of the three ninjas is relatively long in the plot, in addition to the need for the plot to receive a box lunch, I personally think it is difficult to have other inducing factors to cause various unexpected situations in kiba sannin.
In this case, once Tsunade is unable to maintain his appearance (Kishimoto reveals Tsunade's true face), it can also be understood that Tsunade is in a weak position in comparison with the abilities of Tsunade and Ōsakamaru.
This is a gap with Kishimoto's positioning of Kiba Sanshin's strength, in order to avoid the situation that fans believe that Tsunade's ability has slipped sharply because of the disclosure of Tsunade's true face, Kishimoto did not let Tsunade appear in his true face.
Finally, I personally believe that the main reason why Kishimoto did not disclose the true face of Tsunade is to maintain the attention and attraction of young male animation fans who occupy the main position in Naruto.
In addition, in order to reflect the advantages of the Gang Hand in controlling the chakra ability, the true face of the Gang Hand is not disclosed, please forgive me if the analysis is not in place, and you are welcome to leave a message to discuss if you have other ideas.