GBP/JPY is developing impulse wave C (colored light green in the chart) of medium term downtrend from 127.31. Within this wave there are five subwaves (colored royal blue in the chart) with impulse subwave 5 still developing from 124.36.
The targets of the downmove are Fibonacci expansions off 130.81-123.27-127.31, 127.31-124.47-126.55, 126.55-123.04-124.36, 124.36-121.27-122.55, 122.55-120.68-121.40.
Supports:
- 120.24 = contracted objective point (COP)
- 119.77 = objective point (OP)
- 119.53-46 = confluence area of two OP's
- 119.11 = super expanded objective point (SXOP)
- 118.68 = expanded objective point (XOP)
- etc.
If the price reverses to the upside the immediate resistances will be Fibonacci retracements of the wave down from 122.55 - this wave is not developed yet, so no resistances are available so far.

Overbought/Oversold
Assuming that the major wave is down it's preferable to try short positions when the Detrended Oscillator gets above the zero level (5-10 pips above the current prices) or into the overbought area (30-40 pips above the current prices).
Read more on how to apply Fibonacci studies to calculate price targets.