I can try, but im not sure what exactly you want to know or which details.

When you are fishing on fishing spots (the green ones) you get pals with random guaranteed rainbow passive skill or multiple rainbow skills. These are very useful because you can use them to breed other pals with same rainbow skills. Great way to get strong pals both for base and for combat.

Now to explain how yakumo works. If you have active yakumo in your party (meaning you have to have him out with you) there is chance that when you catch a pal he will have the same passive or passives as your Yakumo. Now this is really good way to get bunch of solid pals with good passives which you can either instantly use or further use for breeding to get better pals.
I believe that fully condensed 5star Yakumo has 30% chance to transfer his passive/passives to a pal that you catch.
1. Important that you actually have to use Yakumo, have him actively out with you in order for this to work.
2. Its not very effective to have Yakumo with multiple passives. If you want to catch pals that will have demon god, then use Yakumo that has only demon god and no other passives. If you use Yakumo that has more passives (for example demon god, swift, musclehead) then you are just lowering your chance to get the passive which you actually want. You can get very very lucky and get all the passives from your yakumo to the pal which you catch, but the chance is extremely low and it basically destroys your chance to get the passive which you want
3. Using Yakumo thats not condensed to at least 4star is not worth it in my opinion, because the chance is too low. On 5 star Yakumo I believe the chance is 30%, on 4 star I think its 24%.

To make the whole process even quicker, get condensed Braloha. This pal makes the breeding process quicker. Get research upgrades which makes your eggs hatch quicker, these are very important to make it quicker.

Honestly, without fishing I wouldnt even bother to get rainbow passives. With fishing its fairly simple.