Ono-san has a very focused LV6 build: maximum copies of [BT4-062] Nidhoggmon and [BT5-056] Rafflesimon. His choice of LV6 can offer a lot of board control: Nidhoggmon (being a BT-04 staple) board wipes, while Rafflesimon provides defensive control.
When we take a deeper look at the current meta, Nidhoggmon can be quite the beast. He is very effective against yellow Crusadermon (because Crusadermon always attacks and will almost always be suspended, with a wide board) and Diaboromon (tokens are below 5000 DP) decks. In addition, Shoutmon DX, Hexblaumon and Zwart Defeat will most certainly be suspended, while a wide board of new black blocker Digimons and purple rookies make an easy meal.
Meanwhile, Rafflesimon provides defensive and offensive support at different moments of the game. When the opponent has a relatively narrow board (just a single or 2 Digimons), Rafflesimon can be a very effective disabler. When correctly used, she can encourage the opponent into widening their board, moving into favor of Nidhogg. On the other hand, when your board is sufficiently wide to go on offensive, Rafflesimon can be used to disable an opponent's blocker.
Both choices of these LV6 Digimons provide solutions for both narrow and wide boards, offering solutions to almost any board. Ona-san also plays 2 copies of [BT4-091] Valdur-Arm for additional versatility (especially against BT5 Omegamon) since most Digimons in this deck do not easily go above 15000DP (even when boosted with Rafflesimon or Pokomon).