Yu Kanda

With his ponytail hair, Kanda Yu is often mistaken for a girl, but he truly is a guy. A really sour one, too. Lenalee also made the same mistake when she first met him. Kanda barely talked, but he had a foul mouth. He first joined the Black Order when Lenalee was only 8 years old; which means that he enrolled approximately two years after Lenalee. That makes him one of the people whom Lenalee has known for a really long amount of time.

Kanda is a Japanese. Lenalee learned meditation from him. She always ran over to his meditation place when Leverrier was around. It's probably due to Kanda's introverted personality, who wouldn't ask her questions that might confuse her, that she felt relaxed and calmed down a little more. Silence is golden, huh?

We don't get to see many interactions between these two, because they don't seem to share the same mission frequently. However, judging by the way Lenalee pinched Kanda's cheek in the cover of chapter 156, it seemed that Lenalee is one of the few people that Kanda didn't bother to draw a sword upon. (Of course we know what Komui would do if he were to draw his sword upon her.)

In addition, Kanda seemed to be rather aware of the chemistry between Lenalee and her brother. It's possible because he was already in the Order when Komui finally enrolled and reunited with his sibling.