User blog comment:B214/Question and Answers 3/@comment-4547267-20140704034441/@comment-1359322-20140704075929

Actually i think it's safer to say that Issei and Vali attract people of opposite natures. They are like yin-yang. If Issei attract type-A, then Vali would attract type-B, if Issei attract type-B, Vali would attract type-A.

As Sun Wukong said, "“Sekiryuutei attracts the hearts of people. Hakuryuukou attracts the hearts of the “exiled”. Two-Heavenly Dragons. You guys are Heads and tails. You guys are interesting Heavenly Dragons.”"