Of all the options, why choose one of the ugliest/crapy girls as Colosseum event reward (fun part is they are named oriental "beauties"). AND, not only this but but to upgrade a weak ability (Yakuza) to a slightly more useful one. Comparing damage output to Venom (Sheela na gig upgrade), you can easily make out that it is mythic level crap (This if forcing you to upgrade crap for World Bosses event portal). Sensei is far better than Yakuza both in looks and ability according to my personal opinion.
Please for future ability upgrade, choose Girls which have either good ability (Namaah, Zola) OR are eye candy (like Royal Sluts) so that there is interest in keep playing the game.