Well, you can't force other players to accept Grim attaching himself to them, and if it is in-character for them to be able to resist then they would likely do so. Attacking them in that case is fine, but I don't think it is necessarily reasonable for you to seek to cause them permanent damage.
Grim's entire purpose in life is to find it's one true love and gain more magic too feed off of. If someone gets in the way and it can get back at them by feeding off of their magic or stealing a magical possession, core, circuit, familiar or so such then he would be spiteful enough to want to make them suffer.
(remember how yandere venom got when anything kept it from peter before it went host jumping, imagine that but they are connected to the person both magically and physically and the feel the rejection happening, they will hit back hard)
Grim has the heart of a young maiden looking for love and the fury of a woman scorned after being denied that love. Still genderless though.