This guidance is from SGI President Ikeda’s book The Wisdom for Creating Happiness and Peace, part 2, pp. 54–58.

I would like to discuss the assertion that Buddhism is about winning.

My mentor, President Toda, who often gave guidance on this subject, said: “Faith is a struggle against deadlock—for the individual and for humanity. It is a struggle between the Buddha nature and devilish functions. That is the meaning of ‘Buddhism concerns itself with winning.’ ”

There are bound to be times when we become stalled in our progress. That’s when we need to chant and take action with even stronger determination. When we do so, we will definitely cultivate a more expansive state of life and be able to move forward once again. Continually repeating this process is the heart of our Buddhist practice.

Our victory is determined by whether we win or lose in this struggle with ourselves, with stagnation and with devilish functions. Those who neglect this fierce, unrelenting struggle with their inner weaknesses are already on the path of decline. They treat life like a game. Such complacency is the very hallmark of defeat.
Nichiren Daishonin writes:

Buddhism primarily concerns itself with victory or defeat, while secular authority is based on the principle of reward and punishment. For this reason, a Buddha is looked up to as the Hero of the World, while a king is called the one who rules at his will. (“The Hero of the World,” The Writings of Nichiren Daishonin, vol. 1, p. 835)

Rewards and punishments can be measured by degree and are relative by nature. For example, one can score 10 or 60 out of 100 on an exam, or receive awards of various rankings. In this way, rewards and punishments can be compared with one another as better or worse, because they are relative.

But victory and defeat are absolute. You either win or you lose. There is no middle ground. A Buddha is one who has achieved victory. A “hero of the world”—one of the titles of the Buddha—is an unrivalled champion in the human world, in society.

Various Buddhist scriptures give the Buddha similar names, such as “Victory in Battle,” “Victorious Leader,” “Triumphant Force,” “Superior One,” “Superior Banner,” “Heroic Subduer of Devilish Forces” and “Ten Power–Wielding Conqueror of Devilish Forces.”

In other words, the Buddha is the leader who triumphs in the struggle against devilish functions. Victory attests to the power of Buddhism, the power of faith.
Referring to his battle with devilish forces, Nichiren writes:

The devil king of the sixth heaven has roused the ten kinds of troops and, in the midst of the sea of the sufferings of birth and death, is at war with the votary of the Lotus Sutra to stop him from taking possession of and to wrest away from him this impure land where both ordinary people and sages dwell.

It has been twenty or more years now since I found myself in that situation and began the great battle. Not once have I thought of retreat. (“The Great Battle,” WND-2, 465)

The “ten kinds of troops” refers to various kinds of earthly desires or deluded impulses. The Treatise on the Great Perfection of Wisdom lists them as follows:

1. Greed. (Becoming attached to the five desires and neglecting one’s Buddhist practice as a result.)

2. Discouragement. (Being depressed and listless.)

3. Hunger and thirst. (Being assailed by these desires.)

4. Craving. (Decline resulting from desire or attachment. It includes attachments stemming from love or sexual desire, or addiction to substances such as alcohol or other forms of pleasure-seeking.)

5. Sleepiness. (This doesn’t mean that we are supposed to give up sleep. It refers rather to a lazy and negligent attitude or way of life. It may also include not making any serious attempt to improve oneself and just getting by with the least possible effort.)

6. Fear. (Succumbing to one’s anxieties and being cowardly.)

7. Doubt and regret. (Devilish functions that try to lead practitioners astray and cause them to doubt or regret the path they are pursuing.)

8. Anger. (Allowing angry thoughts to obstruct one’s practice.)

9. Fame, fortune and false glory. (Allowing attachment to material gain and worldly reputation lead one away from the path of attaining Buddhahood.)

10. Arrogance and contempt for others. (Thinking highly of oneself and scorning others.)

This last characteristic of arrogance, incidentally, has been exhibited by all who, until now, have abandoned their practice and attacked the Soka Gakkai. Indeed, they have allowed themselves to be defeated by all ten of the devil king’s armies, captured by them and enlisted in their ranks.

What is the weapon for vanquishing these ten armies? It is none other than the “sharp sword” of faith. That’s why leaders of kosen-rufu need, first and foremost, to be courageous people of strong faith. Otherwise, no matter how excellent and accomplished they may seem, they will not be victorious in the battle against devilish forces at the fundamental level of life. Strong faith is the measure of a truly strong person.

In this passage, the Daishonin asserts that an intense battle is being fought between the Buddha and devilish forces throughout the universe, which Buddhism describes as the “sea of the sufferings of birth and death.”

The entire universe is the stage of a colossal struggle—a struggle between constructive and destructive forces, between the energy toward order and harmony and the turbulence leading to disorder and chaos, between the power of compassion that unites and the power of hate that sunders, between life and death, light and darkness, happiness and misery, advance and retreat, rise and fall, freedom and constraint, hope and despair, the energy to nurture life and the impulse to kill. Do we follow the Law that leads to happiness or become enslaved by the workings of the devil king that seek to darken the world with misfortune?

It is vital that we follow the Law that leads to eternal happiness and build a realm of indestructible and everlasting joy. This is our mission as practitioners of Nichiren Buddhism.

(p. 10)