Name Shinichirou Kudo
Species Simply human ^^ ... he's Shuishirou's grandfather.
Appearance: Short white hair; sporting a beard and simple, "normal" clothing.
Age: Not specified - given he's Shuishirou's grandfather, he must be in his.... 70's?
Serves as: A person who helps making Shuishirou realize his strong feelings for Kohaku.
Talents: Persuading people, inviting himself.

Shinichirou (I swear ONE day I will have a nervous breakdown because of all these oh-so-similiar names) is Shuishirou's (SEE!?) grandfather who moved over to the United States a long time ago, but frequently invites himself over for visits ^^;
Neither occupation nor age (lol at least GENDER though, that's quite something in this series) are stated, but one can safely assume that he's in his 60's or 70's and quite well-off. (Seeing how he arrives with private vehicles all the time O_o;)
Shinichirou can be a bit of a nosy bother to his grandson, but has a good heart. He might want to learn to mind his own business, but in the end he only means well & tries to help his relative.
Despite his age, he is still very energetic and youthful and seems a lot younger than he actually is. He has taken on a strong liking for Kohaku and obviously likes the idea of his grandson spending his life with the angel. Furthermore, he seems to support the idea of Shuishirou finally being part of a "real family" (how the Kudo household can easily be described with all ist various inhabitants), since his mother passed away so early.
Shinichirou doesn't serve as much more than a supporting character who attempts to help Shuishirou in finding to his true feelings.