Rei Passives

One way to explain it: They are weaker manifestations of your zanpakutou's element.

Think Yamamoto's Zanpakutou, his is fire based. Now without going Shikai or Bankai, by flexing his Reiatsu flames come out. What do said flames do? Burn people.

In your character's case, you are utilizing the kinetic aspect of heat from what I glimpsed over. So what would your's be? If you were to increase your spiritual pressure it pushes everything around you away in the form of a constant shockwave. Think of it like being in a wind tunnel that you struggle to push towards. You could be startled and your reiatsu spikes defensively, tossing everything around you away. Useful, and also funny, applications.

What about Toshiro? He makes things cold. Could even go with an aesthetic saying the area becomes frosted over, turning nearby water to freeze or just be a slushy. Think of, well, a slushy you'd get from Dairy Queen or Sonic. Your foe might end up slipping on a slippery surface or just get chilly.

Reiatsu Passives are not meant to kill your foe, unless they are vastly weaker than you are. They are more supportive skills that can be defensive or offensive in nature. Other types beyond offensive or defensive are possible, but that is just two basic examples; As well what I stated above.