We all know it's annoying to get Fire Crystals to level something up to level 10 (Unless you're rich) so I thought of a fair way to counter fire crystals, while having fire crystals still be an option for people with a lot of them; setting priority to items.
What priority does:
Setting priority to an item would stop heat from going to any other item, giving as much heat to the priority item as if everything else was full of heat or at max level. Once it reaches maximum level, there will be a second blue bar overlapping the orange one, sort of like this: http://imgur.com/a/2Wga5
The progress bar would only fill when the item is in priority, and if you take an item out of priority while it is filled, the progress bar will be removed.
What is the progress bar? It counts progress towards a free levelup, and would fill significantly slower than the heat bar, depending on the item's level. Here's how I think how it should scale:
Level | Amount of times slower than heat bar
1 | 1x
2 | 1.5x
3 | 2x
4 | 5x*
5 | 4x
6 | 5x
7 | 6x
8 | 7x
9 | 8x
10 | 10x
*Level 4 should fill slower than 6 because when it reaches level 5 is when most items recieve an upgrade/second ability
I really do like the idea honestly. I would say it's only something that can be done for a single item at a time, hence the 'priority' setting, and that the "level up" should hold no additional bonuses.
However I would also say that critical levels (5 and 10) should not be able to be leveled up in this manner. This would still put emphasis on collecting fire crystals, but make it less forced to collect 400+ for one 5* item.
Alternatively, heating your weapon multiple times increases the chances of every level by a set percentage. Eventually you'll get enough heat to make the lowest option be a 100% chance, but it'll take a while to do so.