GBP/JPY is now moving within impulse wave C of long term downtrend - colored light green in the chart. Within this wave there are A, B and C subwaves with subwave C from 130.82 still developing (colored royal blue in the chart). The latter wave also has its subwaves - A and B colored magenta in the chart. Subwave B is still developing from 124.87.
Now the targets of the upmove are Fibonacci retracements of 130.82-124.87, and expansions off 124.87-128.11-127.15.
Resistances:
- 128.55 = .618 retracement
- 129.15 = contracted objective point (COP)
- 130.39 = objective point (OP)
If the price reverses to the downside the immediate supports will be Fibonacci retracements of 124.87-128.11 and expansions off 139.93-130.26-135.11, 135.11-129.74-132.30, 132.30-128.19-130.82, 130.82-124.87-128.11, 128.11-127.15-127.69.
Supports:
- 126.87 = .382 ret
- 126.73 = OP
- 126.49 = .50 ret
- 126.14-11 = confluecne area of expanded objective point (XOP) and .618 ret
- 125.18 = super expanded objective point (SXOP)
- 124.43 = COP

Overbought/Oversold
Assuming that the medium term trend is down it's preferable to try short positions when the Detrended Oscillator gets above the zero level (current prices) or into the overbought area (20-35 pips above the current prices).
Read more on how to apply Fibonacci studies to calculate price targets.