The reason Todoroki is always in a Tranquil Fury at Deku is because Todoroki is projecting and falsely equating Human Fusion to Quirk Marriages
- It's well known in canon that pretty much all of Todoroki's issues come down to his parents in one way or another. Given how much his dad is a Berserk Button for Todoroki early on and his own loathing of Quirk Marriages - not to mention that Shoto was produced deliberately to have the perfect combination of his parents' quirks - the fact that Izuku's Human Fusion essentially lets him do the same thing by combining and/or upgrading the Quirks of the Fusion Components basically rings all of Todoroki's worst warning bells.
- As evidence, when the students are riding the bus to the USJ the discussion turns to Fusion. After the revelation that Izuku has now also Fused with Mina once, Todoroki deliberately looks over all the girls in class 1-A that Izuku's Fused with before glaring at Izuku, not even seeming to consider that Izuku's also Fused with Bakugou.
Following the above, the way Izuku and Todoroki finally become friends will be by Fusing and each getting a look at the other's perspective.
- It's been implied but not stated anywhere that Deku can't fuse with someone against their will, but this hasn't actually been tested. At some point - if the fic mirrors The Stations of the Canon, then probably during the Sports Festival - Izuku will accidentally Fuse with Todoroki and the Mental Fusion aspect will be how the two realize that there's been a misunderstanding... and how Deku finds out about Todoroki's childhood.
Izuku is going to Fuse with a Villain at some point, and it will be Played for Drama
- Given that in addition to Dragonball Z, Steven Universe is one of the big inspirations for how Izuku's Human Fusion works, there's a great deal of potential for some terrifying Body Horror by forcing Fusions or unwilling Fusions (whether the power activation is accidental or something else) á la the Cluster.
At some point Izuku will Fuse with Toga Himiko
- Seriously. Think about it. All she needs is to successfully pass herself off as someone long enough and Izuku could easily step into it willingly and entirely unaware that it's actually Toga.
- Their Quirk Mutation of Toga's Shapeshifting and Power Copying will result in the ability to turn into any Fusion that Deku has been before. Unfortunately, they will still be as crazy as Toga.
- Flashbang: Can fire light from all parts of his body.
- Ranged Blasts via producing hot or heat absorbing plasma.
- Something related to her secretions cause Tsuzuru's quirk was?
- Better radiator.
- Engines on arms.
- Longer Range.
- X-ray vision.
- Infared vision.
- 360 vison.
- Unbreakable state in base.
- Can absorb more metal into themselves, the more they take in, the harder they get.
- Steel version of Unbreakable.
- Two Tails á la Tails.
- More control over voltage.
- Higher limit before going stupid.
- Turning other objects invisible via touch.
- Sprouting body parts from anywhere on his body.
- Size Shifter for her whole body.
- Ambipom, as in two tails with hands.
- Dark Shadow that can make more of itself.