Radio Storm, Vol. 2 (manga)

Sak has found his caller, a former child soldier that goes by the name of Lima. Much to Sak's dismay, the headstrong Lima is in no rush to return to the academy--a safehaven from the deadly plague that's rapidly spreading. Instead, Lima is more interested in visiting the resting place of an old friend, and Sak who would sacrifice anything for his caller to return his affection, reluctantly agrees. However, Lima's feelings for his new core user are more animalistic, and he'll keep pushing his boundaries knowing that Sak is helpless against him.