Two of the people that have the most 'serious' tone of impact on Murata's character (the two who I would have never suspected would fill those roles):
Ari: Murata’s first intentions when first getting involved with him were purely selfish - the boy reminded him of his very own self and he hated that. He hated how Ari acted reminded him of a part of who he used to be, the part that he was hiding with his constant and often falsely generated cheerfulness. He took it upon himself to try to change that so watching him wouldn’t be so painful. Somewhere along the way emotion set in, (call it love if you will) and Murata realized he cared about Ari more than he let on and more that he had let himself accept. Ari is perhaps the first person in lifetimes that has made Murata feel human and ‘liberated’ from his duty guiding the Maou, and following/questioning Shinou’s orders. When he’s around Ari he’s able to be happy for a reason other than to cover another face or to hope that he’ll come off as normal.
Meer: Murata had/has this sort of pop-star crush on Meer, which he laughs at himself for. After watching her for a while, he noticed her little freak outs and how everybody seems to be alluding to the fact that she is in fact, not Lacus, he starts see her in a more vulnerable light. After the arrival of the real Lacus (whom he greeted personally) he puts the pieces together and understands that Meer is someone very much like him - somebody playing a role to be needed, because the real them isn’t what people want. He understands that it’s easier for her to be Lacus, as it’s easier for him to just be dorky old MuraKen. Until she reveals her real indentity to him personally he’ll always smile and call her “Miss Clyne” for as long as she needs it.