Birchstep is a very prickly cat. You would have to be very persistent or someone he has known well since kithood to really be a friend. However, he is very loyal to every cat in ShadowClan and would not be hard for Birchstep to at least consider any cat in his Clan with good relations.
Enemies
The medicine cat probably has a lot of these. The most well known is the ThunderClan warrior, Shadeclaw, who killed his mentor in a battle between the two Clans (PS this character is up for adoption). Otherwise, Birchstep and other cats might not just get along. He has a habit of insulting people and not apologizing! So this may be the reason they don't like one another.
Love Interests
No thanks~ Birchstep is one, a completely loyal medicine cat and is following his destiny accordingly, and two, asexual.
Plots
I'm open for suggestions! Birchstep is a medicine cat, so these plots could get dramatic and fancy.
Medicine Cat of ShadowClan Mentor to Sycamorepaw Mentored by Breezefoot <perhaps the best damn medic the Clans have ever seen>