Attributing responsibility and freedom within the context of Beloved is unconventional.
Sethe, outcasted and proud, does not seem to feel any responsibility to her community. Before her obsession with Beloved, Sethe had only one true responsibility--protecting herself and her children from slavery (her past). She further found responsibility through work in order to support Denver. This responsibility seems to be a response to her lack of freedom pertaining to the past. Even in the free northern states, Sethe appears slave (ironic) to her past slavery. Without her acceptance of the past, Sethe cannot attain personal freedom.
After the incarnate Beloved is introduced into the novel the one responsibility that Sethe does hold is ignored. She is too obsessed by Beloved and her past that she ignores her responsibilities in reality, even a responsibility to physical necessities and supporting her children by working as she does lose her job. She indulges in her need to be responsible to the past and loses every freedom she has, completely controlled by her loyalty to her guilt.
Only after Beloved vanishes by the support of the community, is Sethe able to find personal freedom. Through the words and support of Paul D who reminds her that "she is her own best thing" and that she has two legs instead of four Sethe learns to forgive herself and move on to create a future in which she is actually free.
Sethe finds a responsibility to take care of herself by and lets go of the past to give her freedom.
Once Beloved becomes incarnate, Denver finds responsibility in protecting her from her mothers possible instability. With this new responsibility and companionship, Denver seems to have found satisfaction, but I would not call it freedom because it is temporary and completely dependent. Unlike Sethe's struggle with the past, Denver's struggle appears to be with identity. When she is with Beloved she fears that she has no self outside of Beloved.
When Denver transitions to protecting her mother from Beloved, she steps into the world, a step of freedom brought on by a sense of responsibility. She asks for work and finds responsibilities within the community and discovers that she must take care of herself--a concept that never occurred to Denver before. In finding her own responsibilities, Denver begins to imagine a future for herself, possibly attending college and being sought after by boys. In talking with Paul D at the end of the novel, Denver is proven the most dynamic character, with a sense of confidence and purpose that come with identity.
Denver found freedom in identity through seeking responsibility.
Between these two contrasting characters, freedom appears to be the responsibility to take care of oneself, in part by providing yourself a future. Freedom is moving forward.