In Weapons of the Gods, you test your abilities by rolling a dice pool of d10s. When you roll your dice, you're looking for matching sets. Should you get a matching set, your result reads as follows: the number of the matching set is the ones digit, while the size of the matching set is the tens digits, so two 5s would read as 25. If you get no matching set, simply use the highest number and use a set of 1, so if you roll 3d10 and get 1-5-8, your highest result would be 18 (one die of

Now, should you roll multiple sets, you can choose to draw one set into "The River", which is a reserve where you can store sets for a later use. For example, if I were to roll 5d10 and get 2-2-5-6-6, my results would be 15, 22, and 26. I can choose to store the 2-2 or the 6-6 into the River for later use. Say I store the 2-2 and later on I roll a 1-2-2-4-5. I can then use one (or both of the 2s) from the River to get a result of either 32 or 42. It's possible to use any stored sets from the River even if there are no other results to match it (in case you make a crappy roll).
The order of using the River is as follows:
1) Produce multiple sets
2) Draw one set into the River
3) Expend one or more result from the River
You cannot replenish the River once filled until you empty it completely. The sets in the River last for only one scene; any sets in the River after the scene is over are lost.
In Weapons of the Gods, starting characters can only hold a matching set of 2 in the River, but as they become more powerful, they can increase the set capacity of the River.
Seeing how similar the dice mechanics are between Weapons of the Gods and OVA, this may be a good way to reproduce those "comebacks" we see in Anime. Basically, whenever you roll multiple sets, you can choose to store ONE DIE from a set of your choosing for later use (such as creating or increasing a matching set). You can only store ONE DIE regardless of how big your set was, whether it was two 6s, three 4s, or five 3s. Once you have a die roll stored, you cannot store any more die rolls until you empty out the one you have in reserve. Also, this stored die lasts for one scene (or combat), so once the scene is over, any die roll you have stored is gone.
Unlike other methods presented, such as with Drama Dice, this method is random, but doesn't expend a resource.
If you want to make this into an ability (something like Heroic Comeback), you can determine that the highest die roll you can store is equal to your Ability Level + 1 (so Heroic Combat +3 lets you store up to a roll of 4 for later use).