Daichi is a very kind and protective person. He is the first person seen in the anime as he takes pictures of the mansion which some students say is haunted., When he learns the truth, the girls decide to help him out. He, like Ai, goes out of his way to help his friends and is likely why the two connect.

In the year 2000, as an adult, Daichi's daughter takes a picture at the beach and he sees the mansion where the girls lived but obviously not in the same location he visited it. He goes to see them and meets Ai who becomes agitated because she doesn't know what to do. At the time she denies any connection, but later when he returns and is attacked by Keith she reveals the truth.

(Source: Wikipedia)