Deep down, there was always a part of Yoshiki that died whenever Ayumi mentioned his best friend Mochida's name. It may not have been fair, but he did more for her than Satoshi would ever dream of doing. Satoshi had Naomi. While Yoshiki had a complicated relationship with a girl he swore to protect, just to be pushed down to the ground, and then be slapped in the face with the word 'Mochida'.
It was Ayumi's goal to notify him once an hour that he'd never compare to Mochida. No matter how many times he'd put his life on the line for her, she just kept pitying herself. Wondering what Mochida would be doing right now. It may have been annoying from time to time, but he didn't care. He loved her. He didn't care she didn't return the feelings.
Time after time again, when she'd get possessed, he'd be there. Not Mochida, him. Despite being terrified, he was there. Whenever she needed a shoulder to cry on, guess who would be there? Him. Mochida wouldn't be there. And the times Mayu wasn't available, he'd be there 24/7.
He took being in Heavenly Host as a chance to prove this to her. To prove Mochida wasn't ever there, only he was. He comforted her, sacrificed his own life. He tried to, so hard, but to no avail. It was a lost cause. But he kept trying. He wouldn't be quitting anytime soon.
Then, Yoshiki left her alone, away from the sludged pool, and told her to call him if she needed anything. While he was searching for something to help, a possessed Ayumi jumped into the pool. Despite not knowing how to swim, he jumped in to save her anyway. Because he loved her.
He tried everything. But her go to word was now apparently Mochida. He saved her when the anatomy model tried to attack her. He'd help her when she was possessed, but nothing. Nothing worked. He was helpless. He couldn't do anything. He was out of options. Completely stuck, in a loop. He felt like a broken record.
Especially when he died in that school. He just wanted to save her.