What went down in full at the end
Spoilers for chapter 12!
- During the events of chapter 7, Kotoko hears of the destination. Planning her murder, she informs herself about Hamaga Island. She may have been there as well. note
- Kotoko proposes that Nozaki will be playing dead again, this time more spectacularly. He is on board with the plan.
- Once at the island, she has Nozaki acting as the belayer, having stolen the equipment before. She gives him the signal. Her clothing gets stained, and has to wear her shirt backwards and inside-out.
- She kills Nozaki, cuts the harness, and descends. She also hides the harness in the sand while keeping the gloves.
- The next day, Kotoko stays inside, doing the dishes with Sally. She momentarily goes out to empty the garbage and removes the plug of the boiler, leaving the cottage out of warm water.
- Kotoko, knowing Tsumugu, asks him to check up on the boiler. This way, she makes it so that no one can check his alibi.
- Shortly after Tsumugu returns, so does the warm water. Kotoko goes out and kills Fumi - it is inferred that she climbed up the building form the outside.
- However, she loses the wire. She wants to retrieve it, but does not want to be suspicious and waits until the body is found.
- When the body is found, Suguha takes the wire, leaving Kotoko unable to retrieve it.
- That night, Sally forces the girls to sleep on 1 room. She learns of Kotoko's mistake and frames Suguha by putting the wire in her bag, knowing that Shun will check them the day after.
- That day, predictably, Shun finds the wire. He lets loose his suspicions on Suguha.
- Sally meanwhile poisons the drink of Hikone, while all attention goes to Suguha and Shun.
- After Hikone dies, Sally goes outside. She retrieves the evidence that killed Nozaki from the sand and hides it in her umbrella (with or without the pole).
- Kotoko observes this from the balcony. She excuses herself by saying that she isn't feeling well.
- Tsumugu and Sosei go and check out the office. Kotoko comes around and goes with them.
- Having gone there before, she has left footprints. To divert suspicion, she goes inside first and uses that as an explanation.
- After Sosei and Tsumugu leave the office, Kotoko tells Sally that they did so. Sally then goes to the office.
- Kotoko may or may not be aware of the fact that Sally was Driven to Suicide, but she was aware that Tsumugu would find out where Sally was.
- She did not expect Sally to be taking the blame for all three murders. If Sally was aware of Kotoko wanting to frame Tsumugu, then she would've put the wire in his bag.
- Either way, Kotoko wants Tsumugu to die along with Sally. She removes the placed chair and knows that if he's alive, she has his fingerprints, along with the weapons. However, he lives and exposes the above.
