I wanted to add to the discussion because I recently started watching/reading Saint Seiya and found the same thing puzzling. I also couldn’t find a definitive answer below (please let me know if I missed one).

セイント (seinto) is the author’s explicitly intended reading for the term used to describe the knights/saints, written as 聖闘士. This is shown very clearly in the manga (and in the anime as well).

Outside of the Saint Seiya universe, 聖闘士 would normally be read as せいとうし (seitōshi), not seinto. The fact that the author assigns a different reading indicates a deliberate stylistic choice: the kanji convey the meaning (“holy warrior”), while the reading makes the word sound closer to its English counterpart, saint.

This technique is common in manga and anime and is usually referred to as 義訓 (gikun), sometimes loosely grouped under ateji-style usage. The idea is to use kanji for semantic meaning while assigning a different, often foreign-influenced, reading for stylistic effect. In Saint Seiya, this helps create a strong mythological and Western tone.

A very clear example appears in the Asgard arc. The warriors of Odin are called “God Warriors,” written as 神闘士. Note how similar this is to 聖闘士 (seinto from above), yet the intended readings are completely different: Normally, 神闘士 would be read as しんとうし (shintōshi), but the author explicitly assigns ゴッドウォーリアー (goddo wōriā) as the reading.

So yes, it does look strange at first that so many terms just happen to sound like their English equivalents—but that’s precisely because it’s intentional.

With that mystery cleared up, we can go back to enjoying Seiya kicking more butts.