IMHO, Why we use Engine flush?
Because if am using Havoline, Castrol, PSO's, etc. mineral oils in my car and after that I know that my car needs superior oils like Fully Synthetic (properties of mineral oils & synthetic oils are quite different). Then before using fully synthetic oil, I've to use engine flush so that it can well drain all the particles of previous oil from the engine.
And once I use engine flush and shift to fully synthetic oil, then it may never need to use it (flush) again. Because fully synthetic oils do the very well cleaning of the engine by themselves and have far better other properties too.
For Mira, the choice is yours
If you want to use fully synthetic oils (which are fuel savers and have longer change intervals too), then 5/40 or 5/30 or 0/20 as well (if the car is new).
Or
Can try 10/40 in fully synthetic or semi synthetic category.
Note: Mechanics / oil shop owners always recommend to use 10/40 or 20/50 for the smaller JDMs for better pick up. But using fully synthetic oils increase the enngine's life & performance for sure for the longer run. Because only pick up is not everything that we need from our car.