The police are investigating Koichi's unnatural death.
"You look upset. Is everything alright?" "I just heard that Koichi died an accidental death and Tofugu went bankrupt. It’s a nightmare."
The news that Koichi met a mysterious and unnatural death shocked the nation.
A strange death is one that doesn't seem right. It's an unnatural death, and probably an accidental death (ie wasn't caused by natural causes).
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.