In this fanfiction, it's possible that their hand - holding moment leads to a series of events where they have to protect each other. Harry might find himself in a situation where he has to save Draco from some Slytherin bullies who don't approve of his new friendship with a Gryffindor. And Draco could in turn help Harry when he's in trouble with some of the more overzealous Gryffindors. This back - and - forth protection could deepen their bond and lead to a complete transformation of their relationship.
One possible plot development is that they form an alliance against a common enemy. Maybe there's a new dark force emerging in the wizarding world, and their combined skills and knowledge are needed. Another is that they start to explore their feelings for each other, which could be more than just friendship. It could be the start of a romantic relationship, which would be a huge change from their traditional enmity.
A plot development could be that their new connection makes them outcasts in their own houses. Gryffindors might not understand why Harry is befriending Draco, and Slytherins could see Draco as a traitor. This could force them to rely on each other even more. Also, they might discover some long - hidden secrets about Hogwarts or their families together. For instance, they could find out that there are ancient spells or artifacts that their families were both involved with in the past.