Fusion settings are a great way to shake up an SI's ability to use their foreknowledge.
Sure, they know one setting. They don't necessarily know the other(s) and they really are going to have to guess how those settings are influencing each other. I had fun with this in Hate has a reason for everything: But Love is Unreasonable - the protagonist knew and was ready for Mobusekai, but was not expecting Hamefura, or the intertwining of multiple characters from other settings. While I'd not say it's on a level with Undocumented Features at all, and I stumbled repeatedly towards the end, the mid-arc dramas where relationships were tangling up were a lot of fun to write and to re-read.
The 'theatre' arc, with the first kidnapping is in many ways amusing because the SI is flirting with treason, with high treason (those who know know) and with his actual love interest, while everything else solves itself based on things set in motion previously. He's very side-character to everything because while he'd had an influence and would continue to do so, events did not require his direct intervention.
Sure, they know one setting. They don't necessarily know the other(s) and they really are going to have to guess how those settings are influencing each other. I had fun with this in Hate has a reason for everything: But Love is Unreasonable - the protagonist knew and was ready for Mobusekai, but was not expecting Hamefura, or the intertwining of multiple characters from other settings. While I'd not say it's on a level with Undocumented Features at all, and I stumbled repeatedly towards the end, the mid-arc dramas where relationships were tangling up were a lot of fun to write and to re-read.
The 'theatre' arc, with the first kidnapping is in many ways amusing because the SI is flirting with treason, with high treason (those who know know) and with his actual love interest, while everything else solves itself based on things set in motion previously. He's very side-character to everything because while he'd had an influence and would continue to do so, events did not require his direct intervention.