Well its more or less for the same reason as having it with Galeforce, because both skills activate during the Player's Phase. Of course you don't have to take my recommendation into consideration, but that doesn't mean Lifetaker should be overlooked.
Lifetaker heals 50% of your health if successfully killing an enemy unit, and benefits for not being a proc skill as oppose to Sol. It is by no means an awful skill in practice.
Have mix feelings about the children features in Fates, and certainly not looking forward in future FE titles. Maybe it was nice back in Awakening, but I wasn't really enthusiastic about Fates.
Oboro because not only does she give solid mods to Shiro, but she makes a reasonable mother-son pairing as Oboro!Shiro imo.
Also, I'm not really a big fan of Takumi x Oboro, so don't get the wrong impression or anything... <_<