Realistic dialogue for him hinges on restraint and implication. He's a character of few words, so every line has to carry weight; think about what he isn't saying. The reader's internal monologue should do a lot of the heavy lifting, interpreting his silences, the slight narrowing of his eyes, the way he might turn his head a fraction. A 'reader' character who chatters nervously or demands emotional validation would feel completely wrong. They need to be observant, patient, and possess a certain stillness themselves to match his energy.
Instead of having him declare feelings, show it through action filtered through the reader's perception. 'He placed the Tenseiga on the ground between them, the gesture as deliberate as a spoken vow.' The dialogue that does exist should be formal, precise, and often indirect. A question like 'Why did you intervene?' carries more tension for a 'reader' character to navigate than any flowery confession. It forces them to justify their presence in his narrative, which is where the real chemistry sparks—not in romance, but in mutual, unspoken recognition.