My Heart Belongs to the Lich

When he was ten years old, his heart disease worsened and the only way for him to survive is Heart Transplant. However, there was no available and suitable heart for him. Until one day, his father started the heart surgery. He didn't know whose heart it was but, he was certain that the owner is dead. Who wants to donate his or her heart for him while he or she still alive, right? Everything went fine for him within eight years. Not until, she appeared in front of him. "You have my heart. You need to take responsibility of me" - Cassandra He was stunned and shocked to see her alive. However, the sutured scar on her chest displayed as evidence of the heart removal from her. One day, he sneakily looked inside her room to check on her and saw her rummaging inside her chest like she's looking for something. His eyes widened and found out that there's no Heart organ inside it. Cassandra looked up and she smiled at him. "This is nothing. As long as you take care of my heart, I will remain by your side forever. If you die, I will also die" ----- Inside the abandoned building, she arrived and saw him being tied up helplessly with blood and bruises on his body. A bomb was placed around him and the only way to take it off is to put heavy object on the seat. Unfortunately, there was no other things around except him and Cassandra. Cassandra untied him and pulled him off out of the seat immediately as she sat on the seat while the bomb was still ticking to a lower number. "What are you doing?!" - Samuel "You need to go! I will be fine! You need to save yourself first!" - Cassandra "I won't leave you. I'll stay by your side!" - Samuel "No!" - Cassandra "But..." - Samuel "Have you remember what I said on the day we meet? As long as you take care of my heart, I'll be by your side forever" - Cassandra Suddenly, Samuel was forcefully thrown out of the abandoned building with an invisible force from behind him as the bombed took off. "CASSANDRAAAAA!!!" - Samuel