I feel a little painful during the first few weeks of commute with bicycle. Just wondering that does it make my butt tighter and sexier?
Since cycling is primarily based on leg strength, which is derived from all parts of the leg (including the glutes or butt muscles), then yes.
Here's a great graphic that shows some of the muscles used during a typical pedal stroke:
And basic anatomy tells us that the muscular system works together so it's virtually impossible to train one muscle exclusively without using others at least minimally.
If it pains because of seating on an improper seat then no, it will not tighten it.
If it pains due to miles of cycling together with standing pedaling uphill, then probably yes.