Shortly after Ahsoka is assigned to Anakin, mini Obi-Wan is sent to Anakin as well because of a paperwork fuckup or something and, while initially protesting, Anakin eventually decides to keep both of them, regardless of what the council says.

+ if both Ahsoka and Obi-Wan being insecure about their places as Anakin's padawans.
+ Also, Obi-Wan being somewhere in the realm or 10-11 and absolutely time compared to Ahsoka being around 14, with Anakin and the 501st and 212th being way overprotective of their itty bitty commanders
Extra bonus if these two are somehow able to stop order 66 and find Palpatine out earlier