Ashe and Wilardo's first encounter was in the mansion. They have both entered the place in search of the witch's heart. Their interactions at first seem rather normal. Despite everybody trusting Ashe easily, Wilardo still has his doubts and is cautious with him. Eventually, his doubts seemed to be true and Ashe wasn't as good as everybody thought that he was. Although, he was more cautious of Noel than Ashe.
At the end of routes, Ashe and Wilardo are often seen fighting each other with a knife and a gun. Due to Wilardo's immortality, he is often the winner of these duels. The motive for Ashe partaking in these duels is always because of witch's heart, but as for Wilardo, it varies. Sometimes, he fights for the treasure just like Ashe, and sometimes it's to keep Claire safe from any harm.
In Sirius's conclusion story, despite Wilardo being badly injured, he still tried to convince Ashe to let go of his wish and stop his attempt at killing Claire. His words were a lot harsher than Noel's, but they still helped in changing Ashe's mind.
Wilashe is the most popular ship on AO3 as of now and has gained a massive attraction due to them being polar opposites and having a rivalry with each other. Their interesting dynamic left lots of room for shippers to interpret things and began speculating on how their relationship would probably go like.