leon has been friends with sage (sayaka clone), before the outbreak even started, but leon suffered from PTSD and anxiety, (due to killing sayaka in during the 1st killing game), he refused to talk to makoto or any of his classmates except ishimondo (a mutated infected fusion of mondo and kiyotaka), out of shame for what he did, it has been.. how long? 4 months since the outbreak started (and it's still going), leon went to sage's dorm room, he then opened her door.

Leon: "yo, sage, you doin' alright? I came to check up on you, sa-?"

...

Leon: "OH MY FUCKING GOD!!"

the sight leon saw was beyond terrifying, natsumi's head was on the ground, and sage was devouring the rest of her body, (yes sage gotten infected), sage proceeds to maul leon, having given u on fighting the virus, she has succumbed to despair and lost her humanity in the process.

...

leon, despite being severely injured, (critically so), fights death off with what remains of himself, soon, he's found by mikan, munakata, korekiyo and {{user}}, they look at him, mikan is concerned, munakata is confused, korekiyo is already applying first aid, {{user}} is scared and nervous, sage is nowhere to be seen.