Question: "Is mindfulness a part of Nichiren Buddhism?"

Questioner: Personally I see the value in being mindful, but I think it can lead to ocd like behavior by making you feel like you always have to police your own thoughts, therefore limiting one's ability to fully live in and enjoy the moment, if that makes sense. But what if anything does nichiren have to say about mindfulness?

Respondant: Self-reflection (the World of Learning) is definitely a part of Nichiren Buddhism. Here is but two examples from Nichiren:

"The Parinirvāna Sutra states: “Those who enter the monastic order, don clerical garments, and make a show of studying my teachings will exist in ages to come. Being lazy and remiss, they will slander the correct and equal sutras. You should be aware that all these people are followers of the non-Buddhist doctrines of today.” Those who read this passage should reflect deeply on their own practice. The Buddha is saying that those of our contemporary priests who wear clerical garments, but are idle and negligent, were disciples of the six non-Buddhist teachers in his day."

"At present the entire body of the Honorable Abutsu is composed of the five elements of earth, water, fire, wind, and space. These five elements are also the five characters of the daimoku. Abutsu-bō is therefore the treasure tower itself, and the treasure tower is Abutsu-bō himself. No other knowledge is purposeful. It is the treasure tower adorned with the seven kinds of treasures—hearing the correct teaching, believing it, keeping the precepts, engaging in meditation, practicing assiduously, renouncing one’s attachments, and reflecting on oneself."

And, in the Lotus Sutra, two Arhats, Ananda and Rahula, stated in Chapter 9, Prophecies Conferred on Learners and Adepts:

"At that time Ananda and Rahula thought to themselves, Whenever we reflect, we consider how delightful it would be if we should receive a prophecy of enlightenment!"

Tientai and his disciples perform(ed) a 21 day repentance ceremony.

The Lotus Sutra ("If one wishes to carry out repentance, sit upright and ponder the true aspect" - Universal Worthy Sutra or epilogue of the Lotus Sutra) and Nichiren ("sit upright and ponder the ultimate reality") teach mindfulness directly. The ultimate mindfulness is sitting upright and chanting Namu Myoho renge kyo to the Gohonzon.