Learn Japanese with Anime - I Never Go Back On My Words. That's My Ninja Way! (NARUTO)

Analysis

まっすぐ自分の言葉は曲げねぇ

ま(ま)っ(っ)す(す)ぐ(ぐ) (adverb) means “straight”.

自(じ)分(ぶん)の言(こと)葉(ば) (pronoun + particle + noun) means “my words”.
自(じ)分(ぶん) indicates the speaker Naruto himself and の is the possessive particle so 自(じ)分(ぶん)の means “my” and 言(こと)葉(ば) means “words”.

は (particle) is the topic particle showing the preceding word is the topic of the sentence.

曲(ま)げ(げ)ねぇ (verb) means “not bend”. It’s the contracted form of 曲(ま)げ(げ)な(な)い(い) which is the nai-form or negative-form of 曲(ま)げ(げ)る(る). It’s a transitive verb which requires an object followed by the を particle so “something を曲(ま)げ(げ)る(る)” means “to bend something”. When the object is “one’s belief, opinion, word, will, decision, and so on”, it means “go back on something” or “take something back”.

So 自(じ)分(ぶん)の言(こと)葉(ば)を曲(ま)げ(げ)る(る) means “go back on my words” or “take back my words”. So it’s actually 自(じ)分(ぶん)の言(こと)葉(ば)「を」曲(ま)げ(げ)ねぇ but Naruto says 自(じ)分(ぶん)の言(こと)葉(ば)「は」曲(ま)げ(げ)ねぇ. を is replaced with は to turn the object into the topic of the sentence. The direct translation would be “as for my words, I won’t take them back”. The meaning is pretty much the same but the object is highlighted by using the は particle.

So ま(ま)っ(っ)す(す)ぐ(ぐ)自(じ)分(ぶん)の言(こと)葉(ば)は曲(ま)げ(げ)ねぇ means “I won’t take back my words”, “I never go back on my words”, or “I keep my words straight”.

それが俺の忍道だ

そ(そ)れ(れ) (pronoun) means “it” or “that” indicating the previous statement, so it indicates ま(ま)っ(っ)す(す)ぐ(ぐ)自(じ)分(ぶん)の言(こと)葉(ば)は曲(ま)げ(げ)ねぇ.

が (particle) shows the preceding word is the subject. When it’s used in the sentence like “Noun A が Noun Bだ” it sounds like “nothing else but Noun A is Noun B” so it’s very exclusive.

俺(おれ)の忍(にん)道(どう) (pronoun + particle + noun) means “my ninja way”.
俺(おれ) is the first person pronoun usually used by men and の is the possessive particle so 俺(おれ)の means “my” and 忍(にん)道(どう) means “ninja way”. It’s a personal rule that each ninja lives by, their way of living as a ninja, their motto or belief.

だ (auxiliary verb) is used to affirm what the speaker said.

So そ(そ)れ(れ)が俺(おれ)の忍(にん)道(どう)だ means “that is my ninja way”.

Difference between 自分 and 俺

自(じ)分(ぶん) is a reflective pronoun which refers back to a person in the context. It’s often translated as “oneself” for the first, second and third-person pronoun. In this case, the whole original sentence is 俺(おれ)はま(ま)っ(っ)す(す)ぐ(ぐ)自(じ)分(ぶん)の言(こと)葉(ば)を曲(ま)げ(げ)ねぇ so 自(じ)分(ぶん) is referring back to 俺(おれ) which is Naruto. If he said 俺(おれ)はま(ま)っ(っ)す(す)ぐ(ぐ)俺(おれ)の言(こと)葉(ば)を曲(ま)げ(げ)ねぇ, it sounds somewhat redundant.

On the other hand, 俺(おれ) simply indicates the first-person “I”. The sentence そ(そ)れ(れ)が俺(おれ)の忍(にん)道(どう)だ has nobody to be referred back to so there’s no need to use 自(じ)分(ぶん).

So when there’s somebody to be referred back to, you use 自(じ)分(ぶん), and when there isn’t, you use the first person pronoun. The same rule applies for the second person pronoun and third person pronoun.